Physiology Unit 2 Pardee

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Homeostasis

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A. Dynamic Status Quo-
1. Incredible chemical and physical reactions and activities occur per second in the body (dynamic); and yet,
2. Measurable parameters remain fixed within set ranges near set-points (status quo)

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B. Mechanism of Homeostasis

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1. Monitoring tissue detects/measures actual value of a parameter
2. Monitoring tissue compares actual value of the parameter to its set point and detects changes from the normal setpoint (stimulus)

3. Effector tissues effect a response to the stimulus as a result of input originating with the montoring system and delivered through a "loop"

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C. Negative Feedback Loop or Mechanism

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1. Stimulus must initiate activities which result in a response (stimulus causes response)
2. The direction of the response is opposite to the direction of the stimulus (i.e. if stimulus is an increase in some parameter, the response will be to decrease the parameter back toward setpoint.)
3. Typical mechanism by which homeostasis is maintained in the body
4. Examples: body temperature; renin/angiotensinogen/aldosterone system for maintaining blood pressure; insulin/glucagon system for maintaining blood sugar level; erythropoietin system for maintaining red blood cell count

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D. Positive Feedback Loop

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1. Stimulus causes response; however, the direction of the response is the same as the direction of the stimulus
2. Example: oxytocin mechanism of childbirth/labor and milk ejection in the breast
3. Typically short lived and must be terminated after completing their task

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E. Renin/Angiotensin/Alsosterone System
(blood pressure too low?)

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1. Low blood pressure results in release of renin by juxtaglomerular cells of the kidney nephrons
2. Renin (protein enzyme) cleaves angiotensinogen (made by the liver) into angiotensin I (10 amino acids)
3. Angiotensin I is cleaved into the 8 amino acid containing angiotensin II by angiotensin converting enzymes (ACE) in the blood vessels of the lungs
4. Angiotensin II stimulates thirst and drinking (increasing blood volume and therefore blood pressure), causes vasoconstriction (increasing resistance and therefore increasing blood pressure), and stimulates the adrenal glands to release aldosterone
5. Aldosterone travels to kidneys through the bloodstream and stimulates the nephron to actively secrete potassium ions (K+) into the urine but to reabsorb sodium and water into the bloodstream, increasing blood volume and therefore blood pressure

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F. Insulin/Glucagon System (1)

(hyperglycemia)

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1. Absorption of glucose (increase of glucose in the bloodstream/ hyperglycemia) results in the release of glucose-dependent insulinotropic peptide (GIP-a hormone) which goes through the bloodstream to the islets of Langerhans of the pancreas and along with high levels of glucose in the bloodstream stimulates the beta-cells to release insulin
a. Insulin attaches to receptors on liver cells (hepatocytes), muscle cells and adipose cells
b. Cells are stimulated to place GLUT proteins into their membranes which permit glucose to be absorbed by diffusion (reducing blood sugar level down to setpoint)
c. Glucose is converted into glycogen in liver and muscle cells and fat (triglycerides) in adipose cells

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F. Insulin/Glucagon System (2)

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. When blood sugar levels are reduced below setpoint (hypoglycemia) alpha cells of the islets of Langerhans release glucagon
a. Glucagon stimulates gluconeogenesis
b. Glucagon stimulates the breakdown of glycogen into glucose which is released into the bloodstream and which elevates blood sugar up to setpoint

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G. Oxytocin System

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1. When fetus enters the cervix of the uterus, stretch receptors send inpulses to hypothalamus
2. Hypothalamus releases oxytocin (a hormone) by way of the posterior pituitary gland into the bloodstream
3. Oxytocin goes to the uterine muscle and stimulates further contraction, pushing the fetus further into the cervix, causing additional stretching
4. Process repeats until birth occurs
5. Nursing baby stimulates nipples, sending nerve impulses to the hypothalamus, which releases oxytocin again from the posterior pituitary gland; oxytocin stimulates ejection of milk into the nipple so it is available to the nursing infant (oxytocin does not cause milk production)

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A. Proteins
(What are proteins composed of?)

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- (composed of amino acids)

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Protein-Functions?

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Enzymes, Hormones, Antibodies, muscle proteins, transport, osmotic pressure in bloodstream, hormone and neurotransmitters, membrane channels & pores,

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Enzymes

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- (composed of amino acids) function of protein

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Hormones

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blood borne messengers (ex: insulin and glucagon) function of protein

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Antibodies

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(protien function) - opsonize (label) antigens (like bacteria, virus, etc) for destruction

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Protein function -muscle proteins

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myosin, actin

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transport proteins

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(lipoproteins aid in the transport of cholesterol in the bloodstream, hemoglobin carries oxygen, myoglobin transfers oxygen in muscle)

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Proteins contribute to the osmotic pressure in the bloodstream

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ex: albumen) and other body fluids; solutes in body fluids.

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g. Proteins act as hormone and neurotransmitter receptors

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insulin receptor

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h. Proteins act as membrane channels and pores

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in cell membrane

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2. Polymers of amino acids (polypeptides) joined together by

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peptide bonds

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a. Primary structure

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refers to the sequence of amino acids in the polypeptide, which in turn determines the shape of the polypeptide and therefore its function. Secondary structure refers to alpha helices and beta sheets, tertiary structure the three dimensional shape or conformation, quaternary structure refers to proteins with more than one polypeptide chain in the structure (ex: hemoglobin)

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b. Three dimensional structure (shape) stabilized by

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hydrogen bonds, interactions between R-groups with each other and with surrounding water; disulfide bonds; hydrophilic/hydrophobic interactions. .

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c. Polymer of amino acids manufactured by

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ribosomes from information contained in DNA and carried to ribosomes by mRNA; manufactured by dehydration synthesis process; polypeptides can be broken down into amino acids by hydrolysis process.

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3. Amino acids have

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amino group (-NH2) and carboxyl group (-COOH) bonded to central carbon atom; amino acids differ in the R-group attached to that central carbon atom