ISSA Personal Trainer Certification - Unit 02 - Basic Anatomy and Physiology

Hormones can act in three ways

- Alter the rate of synthesis of cellular protein - Change the rate of enzyme activity - Change the rate of transport of nutrients through the cell wall

Connective tissue contains one or more of three fibers

- Collagen - Reticular - Elastic

Factors affecting digestion

- Eat slowly, and chew food thoroughly. - Maintain posture in an upright position. Avoid eating while lying down. - Eat several meals of moderate size, as opposed to eating a few large meals. - Eat while calm. Nervousness can affect the movements of the digestive system and cause gastrointestinal disturbances. - Allow some time for digestion to occur. Strenuous physical activities should be avoided directly after eating. - Avoid foods that may irritate the stomach, such as hot spices and alcohol. - Consult a doctor if you think you have a digestive system disorder.

Three types of cartilage

- Elastic - Fibrous - Hyaline

Types of tissues

- Epithelial - Connective - Muscle - Nervous

The training effect does three things for blood vessels

- It enlarges them and makes them more pliable to pressure. - It increases their number for saturation coverage. - It helps keep their linings clear of corrosive materials.

The three main things that the nervous system does for the human body

- It senses changes inside and outside the body. - It interprets those changes. - It responds to the interpretations by initiating action in the form of muscular contractions or glandular secretions.

Three types of nervous tissue

- Neurons - Neuroglia - Neurosecretory

Functions of the digestive system

- Receipt, mastication (chewing), and transport of ingested substances and waste products - Secretion of acid, mucus, digestive enzymes, bile and other materials needed to break down food - Digestion of ingested foodstuffs - Absorption of nutrients - Storage of waste products - Excretion - Auxiliary functions

Two major parts of the nervous system

- central nervous system (CNS) - peripheral nervous system (PNS)

The afferent system—the part of the PNS that sends messages to the CNS—receives messages through three classes of receptors

- proprioceptors - exteroceptors - interoceptors

Two parts of the efferent system in the nervous system

- somatic system - autonomic system

nerve impulse

A brief reversal of the membrane potential that sweeps along the membrane of a neuron.

macronutrients

A category of nutrients: including—carbohydrates, proteins, and fats — that are present in foods in large amounts.

cortisol

A corticosteroid that causes a breakdown of protein in muscles.

epinephrine

A hormone produced by the adrenal gland that causes the flight-or-fight response.

glucagon

A hormone produced by the pancreas that stimulates an increase in blood sugar levels, thus opposing the action of insulin.

growth hormone (HGH or hGH)

A hormone secreted by the pituitary gland that affects skeletal growth rate and bodily weight gain.

fat/lipid metabolism

A metabolic process that breaks down ingested fats into fatty acids and glycerol and then into simpler compounds that can be used by cells of the body for general bodily function as well as energy production.

insulin

A polypeptide hormone functioning in the regulation of the metabolism of carbohydrates and fats, especially the conversion of glucose to glycogen, which lowers the blood glucose level.

tissue

A tissue is a group of closely related cells specialized to perform a specific function. Or a collection of similar cells and their intracellular substances. Tissues are the fundamental units of function and structure for the human body.

distal tubule of the kidney

A twisted, tube-like structure found inside a part of the kidney known as the nephron.

plasma membrane

Also known as the cell membrane. It is a complex structure made up of mostly proteins and a phospholipid bilayer. The phospholipid bilayer (which is made up of glycerol, two fatty acids, and a phosphate group) forms a double-walled balloon-like structure with proteins embedded in these bilayer sheets. The nutritional significance of this structure is that the cell membrane is made up of fatty acids, which are part of the phospholipid bilayer.

ketosis

An abnormal increase of ketone bodies in the body; usually the result of a low-carbohydrate diet, fasting, or starvation.

sympathetic nervous system

An automatic system that speeds up most activities in the body.

hemoglobin

An oxygen-transporting protein found in blood cells.

fatty acid

Any of a large group of monobasic acids, especially those found in animal and vegetable fats and oils.

erythrocyte

Blood cell that contains hemoglobin to carry oxygen to the bodily tissues; a biconcave disc that has no nucleus. Also known as red blood cell.

alveoli

Capillary-rich air sacs in the lungs where the exchange of oxygen and carbon dioxide takes place.

leukocyte

Cell whose primary function is to combat infections; also known as white blood cell.

gluconeogenesis

Chemical process that converts lactate and pyruvate back into glucose.

nucleus

Commonly called the control center of the cell. The nucleus is essentially a cell within a cell, which has a membrane of its own and houses genetic material. The nucleus houses the deoxyribonucleic acid (DNA) of the cell. The nucleus typically functions to initiate production of substances needed by the cell. The nucleus has another important function: It initiates cell division.

Muscle tissue

Comprises approximately 43 percent of an average man's bodyweight and 34 percent of an average woman's bodyweight. Over 600 muscles work together with the support of the skeletal system to create motion. An additional 30 or so muscles are required to insure the passage of food through the digestive system, to circulate blood, and to operate specific internal organs. In exercise physiology, muscles are the main operative tissue, expending energy, generating wastes, and requiring substantial nutrition.

neurons

Conduct nerve impulses, register sensory impulses, and conduct motor impulses. The central neuron body contains a nucleus surrounded by cytoplasm, and two projections at either end. The two types of projections are axons—which generally conduct impulses away from the body of the nerve cell—and dendrites, which conduct impulses from adjacent cells inward toward the cell body.

Tendons

Connective tissue that attaches muscle to bone.

Ligament

Connective tissue that connects bone to bone or bone to cartilage.

neuroglia

Consist of a delicate network of branched cells and fibers that supports the tissue of the central nervous system.

True or False: About 98% of the human body is composed of only six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus.

Correct answer: True

True or False: Excretion is one function of the digestive system.

Correct answer: True

True or False: Hemoglobin is an oxygen transporting protein in red blood cells.

Correct answer: True

The circulatory systems consists of: a. lungs, mouth, throat, trachea, and bronchi b. mouth, esophagus, stomach, and gallbladder c. heart, arteries, and veins d. all of the above e. none of the above

Correct answer: c c. heart, arteries, and veins

The nervous system is made up of the: a. peripheral nervous system b. central nervous system c. proximal nervous system d. A and B e. A and C

Correct answer: d d. A and B

Hormones are classified as: a. steroids b. amino acid derivatives c. peptides d. all of the above e. none of the above

Correct answer: d d. all of the above

The main purpose(s) of hormones is/are to: a. alter the rate of synthesis of your cellular protein b. change the rate of enzyme activity c. change the rate of transport of nutrients through the cell wall d. all of the above e. none of the above

Correct answer: d d. all of the above

The respiratory system is responsible for: a. supplying oxygen to the body b. eliminating carbon dioxide from the body c. helps regulate the body's pH balance. d. A and B e. A, B, and C

Correct answer: e e. A, B, and C

platelet

Cytoplasmic body found in the blood plasma that functions to promote blood clotting.

Reticular fibers

Delicate, supportive fibers of connective tissue that occur in networks and support structures such as capillaries and nerve fibers.

Tendons and ligaments

Flexible, yet strong, they are the strongest connective tissues in the body. Their intercellular matrix consists of a collagen and reticular fiber network, which originates from the cells they surround. Tendons function to connect muscle to bone or other structures. Tendons can be thick, like the Achilles tendon; or they can be thin, like the aponeurosis—a thin layer of connective tissue that covers the skull. Tendons vary based on their location in the body and the demands placed upon them. Ligaments join bone to bone. Ligaments are most commonly found where two bones articulate to form a joint, such as the elbow.

Together, they stimulate blood sugar levels in the body

Insulin increases cellular uptake of glucose. Glucagon performs the opposite function of insulin.

neurosecretory

Large neurons that produce secretions, which travel along neuron axons and are typically released into the bloodstream. They function to translate neural signals into chemical stimuli in the body.

law of gaseous diffusion

Law stating that a gas will move across a semipermeable membrane (e.g., alveolar, capillary) from an area of higher concentration to an area of lower concentration.

interoceptors

Located in blood vessels and viscera, which report inner body sensations such as hunger, thirst, pain, pressure, fatigue, or nausea.

proprioceptors

Located in joints, muscles, tendons, and the inner ear. They are responsible for picking up messages such as body position and movement (kinesthesia).

exteroceptors

Located near the surface of the skin. They receive information from outside the body such as sight, touch, pressure, or temperature.

aerobic

Occurring with the use of oxygen, or requiring oxygen.

anaerobic

Occurring without the use of oxygen.

diastolic pressure

Pressure exerted on the walls of the blood vessels during the refilling of the heart.

glucose

Principal circulating sugar in the blood and the major energy source of the body.

glycogenolysis

Process describing the cleavage of glucose from the glycogen molecule.

Steroidal hormones

Produced from cholesterol in the gonads and the cerebral cortex

Mitochondria

Referred to as the powerhouse of the cell, mitochondria are small, complex organelles that resemble a sausage in shape. They consist of a smooth outer membrane, which surrounds an inner membrane, forming a sac within a sac. The inner membrane is folded like an accordion, and it forms a number of inward extensions called cristae. The enzymes that are essential for making one of the most important biomolecules, adenosine triphosphate (ATP), exist in the mitochondria. It is here in the mitochondria that ATP stores energy which is used to power biological functions. Within the inner mitochondria membrane, catabolic enzymes (which are involved in breaking down of biomolecules) catalyze reactions that provide the cells with life-sustaining energy.

afferent system

Related to the nervous system: The part of the PNS that sends messages to the CNS.

efferent system

Related to the nervous system: system designed to cause action; consists of the somatic and autonomic systems.

peripheral nervous system (PNS)

Relays messages from the CNS to the body (the efferent system) and relays messages to the CNS (the afferent system) from the body.

glycogen granule

Structure of the cell that stores glycogen and enzymes for glycogen breakdown and synthesis.

lymphatic system

Subsystem of the circulatory system, which protects the body against disease.

nervous system

System comprised of brain, spinal cord, sense organs and nerves. Regulates other systems. It is the control center of the body and the network for internal communication.

reproductive system

System consisting of gonads, associated ducts, and external genitals concerned with sexual reproduction.

endocrine system

System consisting of the glands and tissues that release hormones. It works with the nervous system in regulating metabolic activities. The endocrine system helps regulate growth, reproduction, use of nutrients by cells, salt and fluid balance, and metabolic rate.

circulatory system

System consisting of the heart and blood vessels that serves as the transportation system.

respiratory system

System consisting of the lungs and air passageways, which supplies oxygen to the body and removes carbon dioxide.

central nervous system (CNS)

System of the body comprised of the brain and spinal column.

skeletal system

System of the body consisting of bone and cartilage that supports and protects the body.

muscular system

System of the body consisting of large skeletal muscles that allow us to move, cardiac muscle in the heart, and smooth muscle of the internal organs.

digestive system

System of the body consisting of the digestive tract and glands that secrete digestive juices into the digestive tract. Responsible for breaking down foods and eliminating waste.

integumentary system

System of the body consisting of the skin and its associated structures, such as the hair, nails, sweat glands, and sebaceous glands.

somatic system

System responsible for voluntary action - walking, picking things up, etc.

autonomic system

System that processes and activates involuntary action - breathing, digestion, etc.

maximum heart rate (HR max)

The highest rate at which an individual is capable: 220 minus age in years is equivalent to maximum heart rate.

Large intestine and rectum

The large intestine is about 3 feet long. The area where the ileum and large intestine join is called the cecum. The vermiform appendix is also located in this area. In the large intestines some final absorption of water, minerals, and vitamins occurs. Bacteria are present in the large intestine, and through their metabolism, they produce vitamins that are absorbed, such as vitamin K. The large intestine (also called colon) stores the waste products of digestion. When the proper stimulus occurs, the colon empties its contents into the rectum, triggering defecation.

nervous tissue

The main component of the nervous system; the brain and spinal cord of the central nervous system (CNS), and the branching peripheral nerves of the peripheral nervous system (PNS), which regulates and controls bodily functions and activity.

maximal oxygen uptake (V̇O<sub>2 max)

The maximum usable portion of oxygen uptake over a period of time.

glycolysis

The metabolic process that creates energy from the splitting of glucose to form pyruvic acid or lactic acid and ATP.

resting heart rate

The number of times the heart beats in one minute: 72 beats per minute for the average adult. - Conditioned person 60 bpm, times 60 min =3,600 beats per hour (bph) 3,600 bph × 24 h =86,400 beats per day (bpd) - Deconditioned person 80 bpm × 60 min = 4,800 bph 4,800 bph × 24 h =115,200 bpd

Respiration

The overall exchange of gases between the atmosphere, the blood, and the cells.

Pancreas

The pancreas is situated along the small intestine near the stomach and is an accessory organ of the gut. The pancreas produces several secretions that are important for digestion and absorption of the nutrients that are secreted into the small intestine. The pancreas produces another vital secretion to help control carbohydrate metabolism. These hormonal secretions are insulin and glucagon.

left ventricle ejection fraction

The percentage of blood inside the left ventricle pushed out into the body after contraction.

digestion

The process of mechanical or chemical breakdown of food into absorbable molecules.

residual volume

The remainder of the air in the lungs after the usable volume has been measured.

osmosis

The scientific process of transferring fluid between molecules.

contraction

The shortening of a muscle or increase in tension.

small intestine

The small intestine stretches about 12 feet long and is divided into three main regions: duodenum, jejunum, and ileum. The duodenum is connected to the stomach and makes up the first part of the small intestine. The next regions of the small intestine, the jejunum and ileum, are responsible for the majority of nutrient absorption. Instead of being a flat surface, like that of the skin, the small intestine is lined with special cells called villi.

stomach

The stomach is a muscular sac about 2 quarts in volume. It is responsible for the storage and gradual release of food into the small intestine, digestion through chemical secretions and the physical activity of churning the digesting food, and transport of ingested food down the gut. The stomach secretes several types of substances to aid in the breakdown of food. Mucus acts as a protective layer to lubricate the stomach wall and a buffer against acidic secretions. Hydrochloric acid is also secreted in the stomach and helps to keep the stomach relatively free of microorganisms (bacteria) while maintaining the low pH inside the stomach. Hydrochloric acid also acts to catalyze the action of pepsins, which begin the digestion of proteins. The hormone gastrin is also secreted in the stomach and helps regulate stomach secretions during digestion. The enzymes rennin, pepsin, and lipase are also secreted. They function to breakdown or begin the breakdown process of several nutrients. Rennin works on milk protein (casein) to prepare it for pepsin action. Pepsin breaks down protein in the presence of hydrochloric acid. Lipase is the enzyme that breaks down fat molecules.

triglycerides

The storage form of fat made up of three fatty acids and a glycerol group.

vital capacity

The usable portion of the lungs.

stroke volume

The volume of blood pumped out of the heart into the circulatory system by the left ventricle in one contraction.

cytoplasm

This liquid portion of the cell is the site of many reactions, including gluconeogenesis (glucose and glycogen formation), fatty acid synthesis, activation of amino acids, and glycolysis (the first phase of breaking down glucose to make ATP molecules for energy).

Endoplasmic Reticulum (ER)

This organelle forms a network of intracellular canals within the cytoplasm. It exists in two forms: rough ER and smooth ER. Rough ER is ER with ribosomes attached. Here is where proteins and other biomolecules can be made and transported through the ER's canal network to other parts of the cell and outside the cell. Smooth ER is without ribosomes and its function is less clear, although it appears that smooth ER may be the site of steroid synthesis in the testes and adrenal glands. Evidence also indicates that lipid and cholesterol metabolism occur in smooth ER of the liver cells.

Collagen fibers

Tough, strong fibers that form the major fibrous component of the skin, tendons, cartilage, ligaments, and teeth. They are made of the amino acids glycine, proline, lysine, hydroxyproline, and hydroxylysine. Collagen gives connective tissue its versatility because of its ability to interconnect with other molecules and minerals and thereby form an alloy of sorts, with a higher tensile strength than its separate parts. Collagen fibers occur in bundles, which gives it great tensile strength.

adrenal glands

Two glands that release hormones which helps the body cope with stress.

fructose

fruit sugar

The thyroid gland, located in the neck, releases two hormones

thyroxine (T4) and triiodothyronine (T3)

plasma

The fluid portion of blood

Liver and Gallbladder

Digestion is not complete until the nutrients are delivered to the liver and then released into the bloodstream. The intestines are connected directly to the liver by the portal vein. Fats that travel through the lymphatic system enter the bloodstream directly and then are circulated to the liver for processing. The liver cells process the digested nutrients. Some nutrients are used immediately and others are stored for later use. The liver acts as a processing organ that is responsible for maintaining nutrient balance and storing some essential nutrients and glycogen (glucose) for energy. Glucose stored in the liver is used mainly to supply the brain with energy.The gallbladder is a storage sac for a digestive mixture called bile. Bile is a solution of cholesterol, bile salts, and pigments. Bile is secreted into the small intestine in the duodenum. It is essential for the action of lipase, for the digestion and absorption of fats, and for the absorption of fat-soluble vitamins.

Four types of epithelial tissue

Distinguished by the shape of the cells that comprise them: - Squamous epithelium - Cuboidal epithelium - Columnar epithelium - Glandular epithelial cells

Cuboidal epithelium

Epithelial tissue consisting of one or more cell layers, the most superficial of which is composed of cube-shaped or somewhat prismatic cells. Made of cube-shaped cells as found in the lining of kidney tubules.

Epithelial tissue

Epithelial tissue is found throughout the body: as a continuous external layer over the whole body (skin), on most of the body's inner cavities, and making up the body's several glands. On the surface, epithelial tissue functions to protect underlying cells from bacterial invasion, adverse chemicals, and drying. On the inside, it functions as absorbing and secreting tissue, such as in digestive system glands.

Columnar epithelium

Epithelium consisting of one or more cell layers, the most superficial of which is composed of elongated and somewhat cylindrical cells projecting toward the surface. Resembles a column or pillar in shape. These cells are widespread throughout the body, forming linings in the digestive and respiratory tracts. They function as secretory cells or absorptive cells. Some also have small hairs, called cilia, which beat rhythmically and move materials out of a passage, as in the respiratory tract where cilia serve to sweep out foreign matter that may pass into the lungs.

Squamous epithelium

Epithelium consisting of one or more cell layers, the most superficial of which is composed of flat, scale-like or plate-like cells. Composed of one layer of flat cells. It is located in the linings of the mouth, esophagus, and blood and lymphatic vessels. Substances can easily diffuse through this layer of cells.

Elastic fibers

Extendible fibers that are designed to maintain elasticity, thus providing resilience in tissues such as skin, arteries, and lungs.

lipogenesis

The formation of fat

mouth

Food enters the digestive system through the mouth. The mouth has four functions that it exerts on the ingested food. First, the mouth physically breaks apart food by mastication (more commonly referred to as chewing), thus reducing it in size. Second, it mixes the food with saliva, creating a moist mass, called a bolus, which is then made ready for swallowing. The saliva also contains the digestive enzyme ptyalin, which begins the chemical breakdown of starch (carbohydrates). Saliva also serves to lubricate the food for its journey down the esophagus into the stomach. Mucus proteins in the mouth also help the food particles stick together. Third, the mouth regulates temperature by either cooling or warming the food. Temperature regulation is important as enzymes function at their best within a narrow temperature range.

Bones

Form the skeleton, which functions as support and protection for the body. Bone both resembles and differs from cartilage. Bone is similar to cartilage in that it consists more of intercellular substances (matrix) than cells. However, in bone, the intercellular substance is calcified and hardened as opposed to cartilage, which is a firm gel. Calcium salts impregnate and cement the matrix, a fact that explains the rigidity of bones. Embedded in the calcified matrix are many collagen fibers. Bones are not as lifeless as they seem. Within this hard, nonliving, calcified, intercellular matrix exist many living cells. These cells continually receive food and oxygen and excrete their wastes through the numerous blood vessels that are present in bone tissue and bone marrow.

Cartilage

Forms the foundation of bone tissue. It is found at bone ends, in spinal discs, and makes up the soft bony tissue in the nose. Mature cartilage does not contain blood vessels or nerves. It obtains nutrition through small holes that allow nutrients to seep in.

Fibrous cartilage

Found between bones of the spine (disks)

Elastic cartilage

Found in ear and eustachian tubes

Anatomy of blood

Four main constituents: - plasma - erythrocytes - leukocytes - platelets The composition of whole blood is 55 percent plasma (of which 90% is water, 7% plasma proteins, and 3% other), and 45 percent formed elements (of which more than 99% is red blood cells and less than 1% white blood cells and platelets).

Hyaline cartilage

Fund in bone ends, nose, larynx, and trachea

The most abundant hormone produced by the pituitary gland

Growth hormone (HGH or hGH) is the largest and most complex protein created by the pituitary gland.

Lysosomes

Lysosomes are other sac-like structures whose size and shape change with the degree of their activity. They start out small, and as they become active, they increase in size. Lysosomes contain a variety of enzymes, which act as catalysts, directing all major biochemical reactions. These enzymes are capable of breaking down all of the main components of the cell, such as protein, fat, and nucleic acid. The broken-down products formed inside the lysosome can be used as raw materials for synthesis of new biomolecules or for energy. In this way, lysosomes serve to contain and isolate these important cellular digestive enzymes and thereby prevent complete digestion of the cell. They also play a limited role in the engulfing and destroying of bacteria that may enter the cell.

Hormones

Made up of amino acids and can be divided into several classes based on their chemical makeup. The classifications are: amino acid derivatives, peptides/protein, and steroids.

urinary system

Main excretory system of the body, which consists of the kidneys, ureter, urinary bladder, and urethra.

Polypeptide hormones

Manufactured in the many other glands from various amino acid combinations

ribosomes

Ribosomes are extremely small, spherical organelles made up of protein and RNA. They are the most numerous of cell organelles. They are found scattered throughout the cell's cytoplasm and also along the surface of another organelle, the endoplasmic reticulum. Ribosomes function in pairs as two subunits; one subunit is smaller than the other. Ribosomes are located in the cytoplasm and make various compounds from messenger RNA for local cellular needs. Ribosomes situated on the endoplasmic reticulum synthesize compounds for use outside the cell and can be channeled out of the cell for export, such as with hormones and digestive enzymes

Connective tissue

Serves to connect structures and provide support. Connective tissue is composed of cells embedded in a nonliving matrix. The nature of the matrix, rather than that of the cells themselves, determines the function of a particular type of connective tissue. Connective tissue consists predominantly of intercellular material interspersed among relatively few cells. Blood is also considered a connective tissue because it consists of a fluid matrix with cells suspended within. Some types of connective tissue have the consistency of soft gels, which are firm but flexible; others are hard, tough, and rigid.

Glandular epithelial cells

Specialized epithelial cells that secrete bodily products such as mucus and hormones. Secrete mucus and hormones, such as those of the salivary and thymus glands.

deoxyribonucleic acid (DNA)

Strands of DNA form chromosomes. The human cell contains 46 chromosomes—23 matching pairs. Each parent contributes one set of chromosomes from sex cells; 23 come from the sperm and 23 come from the egg. Chromosomes contain the blueprint for all genetic traits, including eye color, hairline shape, and even predisposition to allergies, among many others. Chromosomes are suspended in a liquid called the nucleoplasm.

Golgi Apparatus

The Golgi apparatus consists of stacks of tiny oblong sacs embedded in the cytoplasm of the cell near the nucleus. Research has presented convincing evidence that the Golgi sacs are responsible for synthesis of carbohydrate biomolecules (Cooper, 2000). These carbohydrates are then combined with the proteins made in the ER to form glycoproteins. Glycoproteins play an important part in the function of enzymes, hormones, antibodies, and structural proteins, among other things. As the amount of glycoprotein produced within the Golgi sac increases, the sac becomes inflated. At this point, small spheres form along the surface of the Golgi sac and break away. These globules contain the glycoproteins, which are transported to the cell membrane and then out of the cell into the bloodstream to be used by other cells.

minimum minute volume

The amount of air that a person can process during one minute of vigorous exercise.

Adrenal glands are comprised of two parts

The cortex (outer layer) and the medulla (inner)

Vascularization of the heart

The development of new capillaries and the enlargement of the existing blood vessels. A healthy heart is characterized by a conspicuously favorable blood supply.

The endocrine system works with the nervous system to maintain the steady state of the body

The endocrine system helps regulate growth, reproduction, use of nutrients by cells, salt and fluid balance, and metabolic rate. The nervous system is also important in stress regulation. The endocrine system consists of tissues and glands that secrete chemical messengers called hormones.

esophagus

The esophagus extends between the pharynx and stomach and is the transport conduit for food and water traveling to the stomach. When the bolus enters the esophagus, an involuntary wave of muscle contractions is triggered, propelling the food mass down into the stomach. This muscle contraction action is known as peristalsis. Once at the base of the esophagus, a ring-like muscle (the esophageal sphincter) is reached, which relaxes to allow the food into the stomach.