Homeostasis Test

Question 1

What are the functions of the kidney?

Answer 1

1. Excretion- removal of toxic waste products of metabolism, eg nitrogen containing compounds, such as urea, which is produced by the breakdown of excess amino acids and nucleic acids in the liver
2. Osmoregulation- control and maintain optimal water potential of body fluids under the influence of antidiuretic hormone

Question 2

Why is plasma being filtered into the Bowman’s Capsule under high hydrostatic pressure

Answer 2

1. The renal arteries are wide, short and relatively close to the heart
2. The afferent arteriole of each glomerulus is wider than the efferent arteriole
3. The coiling of the capillaries in the glomerulus, further restricts blood flow, causing increased pressure

Question 3

What are the three layers that separate the plasma from the glomerular filtrate

Answer 3

1. Endothelium of the capillaries, single layer of squamous endothelial cells with pores (more permeable)
2. Basement membrane/ effective filter of the glomerular capillaries- membrane is an extracellular matrix formed from different substances including proteins- prevent large proteins from leaving the blood
3. Inner wall of the bowman’s capsule- consists of specialised cells (podocytes) with foot like processes which surround the capillaries but have spacious gaps- filtration slits

Question 4

What adaptations do the cells lining the PCT have?

Answer 4

-cuboidal epithelium cells
-surface microvilli
-basal invaginations

-numerous microvilli- supply extra ATP for active transport
-CSM contains protein carrier molecules for selective reabsorption

Question 5

What is the function of the DCT?

Answer 5

-consist of cuboidal epithelium cells- with microvilli and many mitochondria

-cells actively pump sodium ions out of the nephron and into the blood
-hydrogen carbonate disaccociates from carbonic acid and passes into blood
-this raises the ph of the blood when necessary
-able to control the acid/ base balance and ionic composition of the blood in the capillaries surrounding the tubule
-from here, toxic substances such as creatanine, can be secreted from the blood into the filtrte for disposal

Question 6

How does the Loop of Henle work?

Answer 6

1. As filtrate moves up, sodium and chloride ions are pumped out of the ascending limb into the tissue of the medulla
2. This creates a salt gradient which produces a region of increasingly negative solute potential in the interstitial fluid in medulla
3. Water moves out of the permeable descenidng limb into the surrounding tissue by osmosis- carried away by the vasa recta- has no effect
4. Filtrate becomes more concentrated as it passes down the descending limb (chloride and sodium ions move in) where it is hypertonic to the blood
5. Called the counter-current mechanism
6. As the collecting ducts pass through this region of high solute concentration, water is drawn out of the collecting ducts by osmosis- more concentrated urine produced