B12 Homeostasis in action

Basic temperature control

Body temperature needs to remain 37 degrees C because this is the temperature at which enzymes work best. 

Core body temperature must be kept stable. 

Body temperature is controlled by the thermoregulatory centre found in the hypothalamus of the brain.

Contains receptors sensitive to temperature of blood around the brain. 

The skin also contains temperature receptors and send nerve impulses to the thermoregulatory centre. 

(very important info, learn all this)

Cooling the body

• Blood vessels supplying capillaries become wider - vasodilation.Lets more blood flow through the capillaries
• More energy transferred from skin to surroundings by radiation - cooling you down. 
• Produce more sweat from sweat glands in skin - water evaporates from skin, transferring energy to the surroundings.

Keeping warm

• Blood vessels supplying capillaries close up - vasoconstriction
• Reduces flow of blood through the capillaries. Reduces energy transfer by radiation.
• Sweat production is reduced - less energy transferred to the environment from evaporation.
• Skeletal muscles contract and relax rapidly - shivering. Shivering movement requires respiration - exothermic process. Energy transfer from exothermic reaction raises temp. 

Cooling = energy transfer to the surroundings     Keeping warm = reducing energy transfer

Removing waste products

• Cells of body produce waste products from chemical reactions.
• Carbon dioxide and urea = main waste products - dangerous if built up for too long.

Carbon dioxide

• CO2 produced as a waste product of respiration. 
• Produces an acidic solution which would affect enzymes if not removed 
• CO2 diffuses out of cells into the blood down a concentration gradient. It diffuses from the blood to air in the alveoli of the lungs. 
• Air containing excreted CO2 is removed from body during exhalation as well as water from lungs.

Urea

• Waste produced by breakdown of excess amino acids in the liver.
• Urea passes from liver cells to blood
• Filtered by kidneys and passed out of the body in urine. 

• Urea is produced when excess protein is eaten or tissues are worn out. 
• Extra protein cannot be stored and has to be broken down. 
• Liver removes amino group from amino acids by deamination - which forms toxic ammonia
• Ammonia converted to urea and passed safely out of body. Rest of the amino acid can then be used.

Maintaining water and mineral ion balance

Water, mineral ions and urea are lost from the body. 

No control - water leaving lungs everytime exhalation happens and lost through skin in sweat. Control - urea, excess water and mineral ions removed from body via kidneys in the urine.

Function of the kidneys

• Kidneys remove excess water, mineral ions and urea from the body
• Kidneys produce urine in which the waste products are excreted
• Short of water = kidneys conserve water and produce little concentrated urine
• Too much water = kidneys produce dilute urine to remove the excess

How do your kidneys work?

Kidneys filter the blood passing through it. Glucose, water, mineral ions and urea all move out of blood into kidney. These substances are passed out in the urine produced by the kidneys.

• Renal artery - brings blood containing bad substances in solution to the kidney
• Renal vein - carries blood away from the kidney, after substances have been removed.

Glucose is reabsorbed back into blood by diffusion and active transport. 

Selective reabsorption = the amount of water and mineral ions taken back in is controlled by ADH hormone.

ADH and water balance 

• In kidney tubules, selective reabsorption of water and mineral ions happens
• Water level in the blood remains constant.
• ADH hormone controls this - secreted by the pituitary gland.

Receptor cells detect concentration of solutes in the blood plasma. 

Water concentration TOO LOW

• MORE ADH released
• Kidneys reabsorb MORE water
• SMALL volume of CONCENTRATED urine produced.

Water concentration TOO HIGH

• LESS ADH released
• Kidneys reabsorb LESS water
• LARGE volume of DILUTE urine produced.

Dialysis

• Machine that carries out the functions of the kidney artificially.
• A person's blood leaves their body and flows between partially permeable membranes. On the other side there is dialysis fluid - fluid contains same concentrations of USEFUL substances as normal healthy blood.
• Kidney failure = buildup of toxic urea and water/mineral ions damage cells by osmosis.
• Treatment by dialysis restores the concentrations of dissolved substances to normal.
• Takes 8 hours, has to be done several times a week with careful protein-less diets because buildup happens between sessions

How dialysis works

• Need to lose excess urea, water and mineral ions but keep glucose and some mineral ions in blood.
• What is lost and kept is controlled by the concentration of susbstances in the dialysis fluid.

Dialysis fluid contains:

• SAME concentration of GLUCOSE and MINERAL IONS as the blood of a healthy person - ensures there is NO NET MOVEMENT OF GLUCOSE OUT of the blood.
• NORMAL plasma levels of MINERAL IONS - means that EXCESS ions can leave the blood by DIFFUSION DOWN A CONCENTRATION GRADIENT.
• NO UREA - makes a STEEP CONCENTRATION GRADIENT for urea to leave the blood. 

Process: blood taken from body down a tube, tube goes into dialysis machine, dialysis machine removes all the excess urea, water and mineral ions in the blood - they diffuse out of it, the clean blood returns back to a vein in the arm. 

Disadvantages: diet controlled, regular sessions (long), tired/unwell, can become hard over time.

Single healthy donor kidney joined to blood vessels of the recipient - replaces diseased kidney. Will work normally, removing urea for almost a decade.

Rejection

• Donor comes from other person.
• Different antigens of donor's kidney to antigens of recipient.
• Antibodies of immune system can attack the antigens of donor kidney = rejection 

Reducing risk of rejection

• Similar tissue type between donor and recipient (meaning antigens are similar)
• Immunosuppressant drugs for recipient to take which prevents immune response.

Dialysis vs Transplant

Dialysis

Advantages of dialysis - Much more readily available than kidney transplants

Disadvantages of dialysis - Have to have special diet , dialysis sessions are long, long-term dialysis is much more expensive

Transplants

Advantages of transplants - free from restrictions of dialysis, eat and drink what you want, cheaper than dialysis in the long rung

Disadvantages of transplants - not enough donors, risk of rejection.