3.7: Homeostasis + kidney

Homeostasis

The maintenance of an organism’s internal environment, within the cells and the body itself.

Dynamic equilibrium

A term describing how the homeostasis occurs in the body, constantly adjusting to changes but kept at a set point.

Set point

The optimum level of body functioning, what homeostasis maintains.

Negative

Type of feedback where homeostasis is maintained. The body reacts to a change from the set point, and corrects back to the set point.

Positive

Feedback that increases changes from the set point - quite rare.

Insulin

Converts glucose to glycogen in order to reduce glucose levels. Occurs alongside an increase in glucose respiration.

Glucagon

Secreted to convert glycogen to glucose, when glucose concentrations are too low.

Excretion

Removal of nitrogenous waste from the body.

Osmoregulation

Control of the enzymes and metabolites (water) concentration to ensure cell reactions occur at a constant and appropriate rate.

Urea

Amino acids are converted to this after deamination, ready to be excreted by the kidneys.

Urine

Urea, creatinine and uric acid are excreted via the kidneys in this compound.

Capsule

Tough outer layer of the kidney.

Cortex

Second outermost layer, where Bowman’s capsule, PCT, DCT, arterioles and glomerulus are located.

Medulla

AKA renal pyramids. Second innermost layer, where loop of Henle and vasa recta are located.

Pelvis

Innermost layer, where urine is collected to be passed to the ureter.

Ureter

Carries urine to the bladder.

Nephron

Blood filtration units, with about a million inside a singular kidney.

Afferent

Type of arteriole that carries blood to the glomerulus.

Efferent

Type of arteriole that carries blood out of the glomerulus.

Glomerulus

A capillary cluster that is surrounded by the Bowman’s capsule.

Bowmans capsule

Surrounds glomerulus, where ultra-filtration occurs.

Proximal convoluted tubule (PCT)

Surrounded by the cortex capillary network, and connects to the descending limb of the loop of Henle. Has microvilli, basal channels, tight junctions and lots of mitochondria and RER.

Distal convoluted tubule (DCT)

Surrounded by the cortex capillary network, and connects to the ascending limb of the loop of Henle.

Loop of Henle

Located in the medulla, and is surrounded by the vasa recta. Made up of the descending limb, hairpin bend and ascending limb.

Vasa recta

Capillary network in the medulla which surrounds the loop of Henle.

Collecting duct

Carries urine to the pelvis, and is responsible for more water reabsorption. Involves hormones.

Ultrafiltration

High pressure filtration of small particles. Occurs in the Bowman’s complex.

Bowmans space

The three layers between the capillary wall and the lumen of the Bowman’s complex; the capillary wall, the basement membrane and the Bowman’s capsule wall.

Fenestrae

Pores in the endothelium cells of capillary walls in the glomerulus, 80nm in diameter. First layer of Bowman’s space.

Basement membrane

Made up of mainly collagen and glycoproteins. Acts as a molecular filter and a selective barrier. Second layer of the Bowman’s space.

Podocytes

Make up the wall of the Bowman’s capsule - squamous epithelial cells. Have projections known as pedicels. Third layer of the Bowman’s space.

Pedicels

Projections of the podocytes. Wrap around capillaries to bring it closer to the basement membrane. They have gaps known as filtration slits.

Glomerular filtrate

Term used for filtered molecules that enter the lumen of the Bowman’s capsule, including water, glucose, salts, urea and amino acids.

30000-68000RMM

Optimum size for molecules to fit though the Bowman’s space and become a part of the glomerular filtrate. Prevents molecules such as blood cells, platelets and large molecules entering the waste material.

Basal channels

Feature of the PCT cuboidal epithelial cells on the side facing the capillaries. Formed via invagination, and increases surface area.

Tight junctions

Formed between adjacent PCT cells, made from multi-protein complexes. Encircle a cell and attach it tightly to neighbouring ones, preventing diffusion between molecules and to the filtrate.

70

Percentage of ions transported from the filtrate back to the blood during selective reabsorption, via some passive diffusion but mostly active transport.

90

Percentage of water transported from the filtrate back to the blood during selective reabsorption, via osmosis. This is due to ion reabsorption lowering the blood’s water potential.

50

Percentage of urea and small proteins transported from the filtrate back to the blood during selective reabsorption. A steep concentration due to the water loss from the filtrate.

Steorotyped

Type of functioning which always acts the same way and doesn’t respond to the body’s needs.

Ascending

Limb of the loop of Henle which is impermeable to water and actively transports ions into the medulla tissue fluid. Has a high water potential and low solute concentration at the peak.

Descending

Limb of the loop of Henle which is permeable to water and ions. Water leaves via osmosis to the medulla tissue fluid. Has a low solute concentration and high water potential at the peak.

Hairpin bend

Apex of the loop of Henle. Has the highest solute concentration, due to the countercurrent multiplier mechanism.

Countercurrent multiplier

Mechanism utilised by the loop of Henle. Limbs move in parallel directions, and solute concentration in the apex is therefore multiplied.

Hypothalamus

Where the osmoreceptors are for the maintenance of the water potential in the blood. The receptor and coordinator for osmoregulation.

Posterior lobe of pituitary gland

Releases (or stops releasing) stored ADH into the blood. The effector for osmoregulation.

Antidiuretic hormone

ADH. A hormone which increases the permeability of the collecting duct and DCT to increase the water potential of the blood.

Aquaporins

Intrinsic membrane proteins with a pore for water to move through, single file. Has 13 types - 6 are in the kidney. They are fused into the cell membrane using vesicles.

Adenyl cyclase

Enzyme which catalyses the production of cyclic AMP, the second messenger. This triggers the release of ADH containing vesicles.

Cyclic AMP

Secondary messenger for aquaporin release, the production is catalysed by adenyl cyclase.

Anti-diuretics

Compounds which increase ADH production, therefore increasing membrane permeability, and water content of blood. However, causes production of low amounts of urine and can cause haemolysis.

Diuretics

Compounds which decrease ADH production, therefore decreasing membrane permeability and water content of blood. However, causes production of large amounts of urine and causes dehydration.

Diuresis

Production of large amounts of diluted urine.

Calcium channel blockers

Drugs which dilate blood vessels to reduce blood pressure.

Beta blockers

Drugs which reduce the effects of adrenaline as this can increase heart rate.

Potassium

High concentrations of this ion causes heart arrhythmias, so intravenous calcium is used to stabilise heart muscle membranes. Glucose and insulin are also used.

Bisphosphates

Administered during kidney failure treatment to reduce activity of osteoclasts, which are cells that break down bone to recycle. This allows calcium to accumulate in bone instead of the blood, preventing heart disease and kidney stones.

Haemodialysis

Type of dialysis where blood is pumped out to a machine with dialysis fluid and tubing to mimic kidney function. Must be done around 3x a week. Sensors in the dialysis machine detect haemoglobin which would diffuse through if red blood cells were damaged.

Continuous ambulatory peritoneal dialysis

Type of dialysis which can be done during everyday life. The peritoneum is utilised as a dialysis membrane, and 4x a day dialysis fluid is pumped through and then removed after 40 minutes. Can cause oedema and potassium ion accumulation.

Iliac

Blood vessels in the groin that the renal blood vessels are attached to during a kidney transplant. Attached first, and the ureter is later attached once urine is produced.

Anti-virals

Administered after a transplant to lower transmission chances of diseases from donor to recipient. An example is cytomegalovirus.

Human leucocyte antigens

Most of these need to be compatible for a viable organ donation, alongside compatible ABO groups.

Immunosuppressants

Drugs which suppress the immune system in order for a transplant to work. Can lead to recipients developing infection (especially of the urinary tracts), therefore low dose antibiotics can be administered.

Transanimation

An enzyme catalysed reaction where an amino group is transferred to a-keto acid, forming an amino acid. For example, ammonium ions and glutarate makes the amino acid glutamate.

Glutamate

Made by the transamination of a-keto group glutarate with ammonium ions. Can be transanimated to make any amino acid. Used by plants to stop waste production.

Ammonia

Highly soluble and toxic waste product excreted by aquatic organisms. Diffuses out rapidly to below toxic concentrations.

Uric acid

Almost insoluble and non-toxic product excreted by birds, reptiles and insects. Used to reduce weight and water loss, but has a high energy cost.

Xerocoles

Desert animals which have adapted to their environment. Often nocturnal or hide underground/ in crevices during the day. Some only live off metabolic water produced during respiration.

Cortical

Type of nephrons with their glomerulus high in the cortex, and a short loop of Henle which barely penetrates the medulla. Most of human nephrons, and are in other animals which have access to a lot of water and produce dilute urine.

Juxtamedullary

Type of nephrons with their glomerulus close to the cortex-medulla boundary, and a long loop of Henle which deeply penetrates the medulla. Used by mammals in dry habitats.

Glomerulosclerosis

Condition caused by high glucose concentration in plasma. Glomeruli lose protein, such as albumin, into the filtrate. Some proteins even link together.

Deamination

Removal of the amino group. Done to proteins to create urea.

Secretory granules

Carry ADH along axons to the posterior lobe of the pituitary gland from the hypothalamus. This triggers ADH to be released into the bloodstream.

Filtration slits

Gaps between the pedicels, where filtrate is able to move through.