Anatomy and Physiology - Lesson 1

Negative feedback

A change in a homeostatically controlled factor triggers a response that seeks to restore the factor to normal by moving the factor in the opposite direction of it's initial change that is, a corrective adjustment opposes the original deviation from the normal desired level. Homeostatic control mechanisms operate predominately via negative control. In negative feedback, a change in a homeostatically controlled factor (O2, CO2, pH , water etc.) triggers a response that seeks restoration in that factor to normal by moving the factor in the opposite direction of its initial change. For example, if CO2 levels go above 45 mmHg the respiratory centres will respond and respiration will increase to remove the excess CO2 in the body. This process will continue until normal blood CO2 levels are achieved.

Temperature

Body cells function best within narrow temperature range (36.4°C-37.1°C). If they get too cold cell function slows down, if they get too hot their structural and enzymatic proteins become impaired or destroyed.

Concentration of water, salt and other electrolytes.

Both water and salt impact on the volume of the cell, thus these two components need to be tightly controlled, as the cells do not function properly if they are swollen or shrunken.

Positive feedback

By contrast the output enhances or amplifies a change so that the controlled variable continues to move in the direction of the initial change. Positive feedback occurs when the initial trigger seeks to reinforce the initial response. Biologically, this does not happen in too many physiological systems: one example of this is during pregnancy. During birth and labour the hormone oxytocin produces powerful contractions of the uterus. As the contractions push the baby against the cervix this stretching triggers a reflex that results in more oxytoxin, thus triggering further contraction of the uterus. This positive feedback event will continue until the stimulus (baby being born) is finished.

Concentrations of oxygen and carbon dioxide

Cells need oxygen (95-100mmHg) to carry out metabolism and the carbon dioxide produced from these chemical reactions needs to be removed. The carbon dioxide (35-45 mmHg) in blood needs to be maintained within normal limits as it contributes to acidity of the internal environment.

The Tissue Level: Tissues are groups of cell of similar specialisation.

Cells of similar structure and function combine to form tissue. There are four primary types of tissue: muscle, nervous, epithelial and connective tissue.

Homeostasis regulated factors

Concentration of nutrients Concentration of oxygen and carbon dioxide Concentration of waste products PH Volume of pressure Temperature

Muscle Tissue

Consist of cells specialised for contracting which generates tension and produces movement. The three types of muscle tissue include skeletal muscle, which moves the skeleton. Cardiac muscle, which pumps blood out of the heart. Smooth muscle, which controls movement of contents through hollow tubes and organs, such as movement of food through the digestive tract.

Epithelial Tissue

Consists of cells specialised for exchanging materials between the cell and its environment. Any substance that enters of leaves the body proper must cross an epithelial barrier. Epithelial tissue is organised into two general types of structures. Epithelial sheets are layers of tightly joined cells that cover and line various parts of the body. Secretory glands, glands are epithelial tissue derivatives for secreting. Secretion is the release from a cell, in response to appropriate stimulation, of specific products that have been produces by the cell.

Nervous Tissue

Consists of cells specialised of initiating and transmitting electrical impulses, sometimes over long distances. These electrical impulses act as signals that relay information from one part of the body to another. Such signals are important communication, coordination, and control in the body. Nervous tissue is found in the brain, spinal cord, nerves and special sense organs.

The body systems contribute together to maintain homeostasis of the human body. To carry the intricate processes of homeostasis the body system must

Detect deviations from normal in the internal environment that needs to be held within normal limits, integrate the information with any other relevant information, and respond appropriately through making the necessary adjustments to the body parts that need to be restored.

The Plasma Membrane

Functionally, the plasma membrane facilitates contact with other cells, provides receptors and mediates the passage of materials. The membrane's selectively permeable nature restricts the passage of certain substances. Substances can pass through the membrane depending on their molecular size, lipid solubility, electrical charge and the presence of carriers.

Homeostasis control systems

Grouped into two classes - Intrinsic means within and extrinsic means outside of. Intrinsic controls are built into or are inherent in an organs. Extrinsic controls are regulatory mechanisms initiated outside an organ to alter the organs activity.

Homeostatis

Homeostasis is defined as maintenance of a relatively stable internal environment. Body cells can function only when the extracellular fluid is compatible with their survival, thus the chemical and physical state of the internal environment must be maintained within narrow limits.

DNA has two important functions

It directs proteins synthesis and is it a genetic blueprint during cell reproduction. Furthermore, in the reproductive cells (eggs and sperm), the DNA blueprint passes on genetic characteristics to future generations.

Organ Level

Organs consist of two or more types of primary tissue organised to perform a particular function. The stomach is a good example because it consists of all four primary types of tissue. The function of epithelial tissue in the stomach is secretion, protection and absorption. The connective tissue provides structural support while the muscle tissue contracts and mixes ingested food before it provides the movement to push the digested food out of the stomach and into the intestines. The nervous tissue controls muscle contraction, coordination and gland secretion with the help of various hormones.

Physiology and Physiologists

Study of the functions of living things. Physiologists explain body function in terms of the mechanisms of action involving cause and effect sequences of physical and chemical processes.

Anatomy

Study of the structure of the body. Anatomy and phsiology are closely interrelated because body functions highly depend on the structure of the body parts that carry them out.

The Cellular Level: Cells are the basic units of life

The cell is the smallest unit of life capable of carrying out the processes associated with life and are the fundamental unit of both structure and function in a living being. All cells, whether they exist as solitary cells or as part of multicellular organism, perform certain basic functions essential for their own survival. The basic cell functions are essential for survival of the individual cells, whereas the specialised contributions and interactions among the cells of a multicellular organism are essential for the survival of the whole body.

Principles of cell theory

The cell smallest structure and functional unit capable or carrying out life processes The functional activities of each cell depend on the specific structural properties of the cell. Cell are the living building blocks of all multicellular organisms. An organism's structure and function ultimately depend on the collective structural characteristics and functional capabilities of it's cell All new cells and new life arises only from preexisting cells Because of this continuity of life, the cell of an organism are fundamentally similar in structure and function

Level of Organisation in the Body

The chemical level, the cellular level, the tissue level, the organ level, the body systems level, the organism level

Body systems contributions to homeostasis

The circulatory system, heart blood vessels and blood. The digestive system, mouth, oesophagus, stomach, intestines and related organs. The respiratory system, lungs and major airways. The urinary system, kidneys and associated "plumbing" The skeletal system, bones and joints The muscular system, skeletal muscles The integumentary system, skin and related structures The immune system, white blood cells and lymphoid organs The nervous system, brain, spinal cord, nerves and sense organs The endocrine system, all hormones - secreting glands The reproductive system, male and female gonads, testes and ovaries and related organs.

Organism Level

The highest level of organisation is the organism level. All the parts of the body functioning with one another constitute the total organism: one living individual. The individual body is made-up of living cells organised in to life sustaining systems. The different body systems do not act in isolation from one another, they depend on the interplay among the multiple systems.

Ph

This needs to be maintained within normal limits (7.35-7.45) in order for enzyme systems and nerve cell function to operate efficiently.

The Chemical Level: Various atoms and molecules make up the the body

Various atoms and molecules make up the body. The most common atoms in the body are oxygen, carbon, hydrogen and nitrogen which make up approximately 96% of the total body chemistry. These common atoms combine to form the molecules of life, such as proteins, carbohydrates, fats and nucleic acid.

Body Systems Level

While the body should always be regarded as a well integrated, functioning unit, within it a number of systems can be identified. For example, there is a cardiovascular system (or circulatory system) that consists of the heart, blood vessels and blood, with its main physiological purpose being to circulate the blood around the body to supply oxygen, glucose and other important nutrients. The digestive system consists of the mouth, pharynx, oesophagus, stomach, small intestine, large intestine, salivary glands, pancreas, liver and gallbladder. These digestive organs work together to metabolise food so it can be broken down into smaller molecules, transported into the blood and distributed to the rest of the cell. In total you will learn about 11 body systems. Incidentally, some texts and website will identify fewer or more systems, depending on how they wish to define them.

Connective Tissue

is distinguished by having relatively few cells dispersed within an abundance of extracellular material. Muscle, nervous, epithelial and connective tissue are the primary tissues each consisting of an integrated collection of cells with the same specialised structure and function.

Lumen

is the cavity within a hollow organ or tube.

Three types of RNA

messenger RNA, ribosomal RNA and transfer RNA.

Homeostatic control is carried out via two processes

negative and positive feedback.