Muscular System

The large intestine

*also called the colon *the place where the large intestine and small intestine are connected is called the cecum, which is a small pouch with an extension called the appendix *the main function of the large intestine is to absorb the remaining water (not absorbed by the small intestine). By removing water a solid mass is formed called feces *at the end of the colon is the rectum, where feces are stored until they are eliminated

Carbohydrate Digestion

*broken down in the mouth by salivary amylase and in the small intestine by pancreatic amylase

Smooth Muscles

*found in the walls of the stomach, intestines, blood vessels, and most internal organs *involuntary muscle *called smooth muscle because it is not striated *functions include moving food through the digestive system and opening and closing the pupil in response to light *slow contractions, but can be sustained for long periods of time

Sarcomere Structure

*made up of thin filaments called actin and thick filaments called myosin *the borders of the sarcomere are called the Z-line *in the middle of the sarcomere where only thick filaments are located is called the H zone *the repeating bands of actin and myosin created the striated look

Cardiac Muscles

*makes up the walls of the heart *involuntary (the heart contracts automatically over 100,000 times a day) *striated *fibers are fused together providing great strength *with each contraction of the heart, blood is forced out of the heart and into the arteries of the body

Nuclei Acid Digestion

*nucleases breakdown (hydrolyze) DNA & RNA into nucleotides

Fat Digestion

*occurs in the small intestine *lipase hydrolyses fats

Protein Digestion

*protein digestion is started in the stomach by pepsin *in the small intestine the pancreas secretes typsinogen and chymotrypsinogen which breakdown proteins *dipeptidase, carboxypeptidases & aminopeptidases break off individual amino acids from a polypeptide chain

Skeletal Muscles

*responsible for moving parts of the body *voluntary muscle *striated (the muscle has a striped look to it) *made up of elongated cells called muscle fibers (about the same diameter as human hair) *longer than cardiac or smooth muscle *capable of strong contractions for a short time

The Stomach

*stores food for approx. 3-6 hours *the stomach secretes gastric juice, a digestive fluid (hormone) that breaks down meat and plant material along with killing bacteria *gastric juice has a pH of 2 which makes the stomach very acidic *the gastric juice also contains an enzyme called pepsin *pepsin has a very low optimum pH and is used to hydrolyze proteins *mixing of fluids with food results in a substance called chyme *the chyme then leaves the stomach and enters the small intestine through the pyloric sphincter

The small intestine

*where most breakdown of macromolecules in food occurs and most nutrients are absorbed into the blood *the first section of the small intestine is known as the duodenum *the rest of the small intestine (jejunum & ileum) is involved in the absorption of nutrients and water

Functions of the Muscular System

1. helps in movement 2. pushes substances, such as food and blood through body 3. helps maintain posture and joint stability 4. heat production (85% of the body's heat)

The Steps of Muscle Contraction

1.) a message is passed from neuron to neuron until it reaches a motor neuron 2.) the motor neuron releases the neurotransmitter acetylcholine 3.) the acetylcholine diffuses fro the neuron to the muscle fiber (20nm) and causes an action potential to move into the muscle fiber through transverse (T) tubules 4.) the action potential causes the sarcoplasmic reticulum (a specialized type of ER) to release calcium (Ca 2+) into the cytosol 5.) the Ca 2+ binds to a protein complex on the muscle fiber called a troponin complex 6.) the troponin complex changes shape and moves the position of the regulatory protein tropomyosin allowing muscle contraction to occur *when tropomyosin covers the binding sites muscle contraction CANNOT occur 7.) part of the thick myosin filament (called the myosin head) converts ATP into ADP and is now in a high energy configuration 8.) the myosin head binds to the actin ( at the myosin binding site) forming what is called a cross-bridge 9.) the myosin head releases ADP, relaxes, and pulls the actin filaments toward the center of the sarcomere causing the muscle to become shorter (contraction) 10.) myosin binds a new ATP molecule and causes the actin to be released and the muscle to become longer (relaxation)

Muscle Structure

A muscle is made up of densely packed groups of elongated cells called Fascicles Each fascicle is made up of smaller units called muscle fibers (a single cells with many nuclei). A muscle fiber is made up of even smaller units called Myofibrils

Sources of ATP

A typical muscle fiber at rest contains only enough ATP for a few contractions. The energy needed for repeated contraction is stored in creatine, phosphate, and glycogen

Glycogen

broken down to glucose which is used in glycolysis and anaerobic respiration to make ATP

Creatine

compound that can quickly make ATP by transferring a phosphate group to ADP *taking creatine supplements help provide more ATP

Muscle Structure Diagram

muscle-->fascicle-->muscle fiber-->myofibril-->sarcomere *Each myofibril is made up of repeating units called sarcomeres, which are made up of two types of protein filaments; thin filaments and thick filaments

Myosin

protein filaments in muscle cells that make up the thick filaments that aid in muscle contraction

Actin

protein filaments in muscle cells that make up the thin filaments that aid in muscle contractions

I band

the area near the edge of the sarcomere where there are only thin filaments

A band

the broad region of a sarcomere that corresponds to the length of the thick filaments of myofibils

Sliding-Filament Model

the theory explaining how a muscle contracts, stating that thin filaments, slide across thick filaments, shortening the sarcomere

Duodenum

where the chyme mixes with secretions from the pancreas, the gall bladder, and intestine itself *the pancreas secretes pancreatic juices, which help breakdown carbohydrates, fats, and proteins that are in the chyme *the liver secretes bile, which helps digest fast gall bladder - stores bile