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What is physiology?

Physiology is the study of how individual organ systems within the body function, and how such individual functions integrate so as to allow the animal to adapt to a changing internal or external environment.


What is the main function of the kidney?

Maintain homeostasis


What is homeostasis?

The tendency to maintain relative constancy of physiological variables (i.e. internal stability) despite large external fluctuations


What did Galen wrote about urine before the 200s.

"the amount of urine every day shows clearly that it is the whole of the fluid drunk which becomes urine, except that which comes away with the dejections or passes off as sweat or insensible perspiration. This is most easily recognized in winter in those who are doing no work but are carousing, especially if the urine be thin and diffusible; these people rapidly pass almost the same quantity as they drink."


What did Claude Bernard famously say?

Claude Bernard (18th century physiologist) « La fixité du milieu intérieur est la condition de la vie libre ».


Name the 3 characteristics of kidneys as an organ

The kidney is an organ that is:
- Regulatory
- Excretory
- Endocrine


Name the 6 characteristics of homeostasis

1. Steady state
2. Set-point
3. Negative feedback
4. Positive feedback
5. Error signal
6. Physiological range


What are the advantages of being multicellular?

Division of labour between different cell types
 Unicellular organisms have one cell do everything (take in nutrients, metabolize them, excretes wastes… --> less opportunity for specialized function; e.g. neurons sending info from one region to another)
 Specialized cells usually require a specific and constant set of conditions (e.g. solute and ion concentration is different inside vs outside cells)
• E.g. neurons need gradient for excitability and action potential, need high Na and K
- BUT... Requires body fluids that have a stable composition and osmolality


What are 2 strategies to maintain gradient against outside environments?

o Minimize gradient – (e.g. sharks taste like urea +++ because sharks use urea as an osmolyte to counterbalance the high osmolality of seawater. They have similar plasma Na and Cl to us but yet they need to live in very high NaCl concentration. They minimize the gradient with urea.)
o Lower permeability (barrier between outside and outside low leakage)


Name 4 examples of animals living in aquatic environments that have adapted to maintain salt gradient.

 E.g. sharks taste like urea +++ because sharks use urea as an osmolyte to counterbalance the high osmolality of seawater. They have similar plasma Na and Cl to us but yet they need to live in very high NaCl concentration. They minimize the gradient with urea.
 E.g. Ionic strength very low in freshwater – have special mechanism to uptake Na and Cl from environment, otherwise they would deplete.
 E.g. Brine shrimps drink large amounts of surrounding fluids and have a salt gland that allows them to secrete salt with active transporters (“purification system”)
 E.g. saline mosquito larvae have a tubule structure (similar to kidney) that actively secretes K, Cl, Mg and SO4 in the tubule, connected to gut, then further modified. This makes them be able to live in very salty and/or very alkaline conditions.


Name an advantage of being terrestrial

More availability of oxygen (< 1% in water)


Name a disadvantage of being terrestrial. How do animals do to prevent dehydration in dry environments?

More possible dehydration

 E.g. Waxy monkey frogs live far away from water in hot environments; conserves water by increasing barrier function of skin (have glands that secrete waxy substance to cover surface – prevents evaporation) – increase resistance to evaporation
 E.g. water-holding frog (Australia) lives in desert – behavioural strategy (stands in cooler areas away from sun to prevent evaporation) but also have a bladder that makes up 1/3 of BW; use it as a water tank and supply to maintain equilibrium
 E.g. kangaroo rats never drink water, thus their water comes from the food (metabolize CHO  CO2 + H2O) = main water supply (90% comes from metabolism and 10% only from the actual moisture in food). Losses only 25% renal and 70% respiratory and 5% feces. Have VERY long loops of henle (inner medulla) for water conservation.
 E.g. beaver kidneys have very short nephrons and no inner medulla. Only outer medulla and a huge cortex. Beavers never have to conserve water because they live in freshwater. Thus, doesn’t need loops of henle for water conservation and concentration of urine.
 E.g. rabbits have a mix of long and short loops (like humans) – short loops clean the blood.


Name strategies to maintain ionic and osmotic gradients

many strategies are used to maintain ionic and osmotic gradients including reduced permeability of epithelial surfaces, specialized excretory organs and secretory glands, behavioural and other adaptations


Name 3 functions of the kidney



Name 6 things that the kidneys regulate to maintain homeostasis

a. ECF volume – maintain perfusion to the brain
b. ECF osmolality
c. Composition of body fluids
d. Blood pressure (linked to ECF volume)
e. RBC mass – through effect on EPO
f. Skeletal integrity – through calcium regulation


Name 3 ways in which kidneys maintain the composition of body fluids

i. Acid-base status (effect on bicarbonate transport)
ii. ECF K+ concentration (very tight regulation) – secretion of potassium by distal tubule
iii. Divalent ion concentration (Ca, Mg, …)


What do kidneys excrete? (4)

a. Nitrogenous wastes – toxic if not excreted
b. Dietary end products
c. Drugs and drug metabolites
d. Products of metabolism


Name 3 hormones secreted by the kidneys

a. Erythropoietin (EPO) – stimulates bone marrow
b. 1,25-OH Vitamin D – active form of VD
c. Renin – catalyzes formation of angiotensin I in RAAS


Which other compounds do kidneys synthesize?

The kidneys are also important sites of metabolism, synthesizing important compounds such as ammonia from glutamine and, under some circumstances, glucose from lactate.


What is the kidney covered by?

The kidney is covered by a fibrous capsule (protective fibrous material)


What connects the kidey to the ureter?

renal pelvis


What is the spot at which the renal artery, vein and pelvis join the kidney.?

The hilus


What connects the kidney and the bladder?

The ureter


Name the 3 major regions of the kidneys and their sub-regions.

1) the cortex,
2) the medulla (pyramid) which consists of the
a. "outer medulla", which is made up of the "outer stripe" and "inner stripe", and
b. "inner medulla", which includes the papillary region
3) the calyces and pelvis, which connect with the ureter


How many pyramids do rats have? Humans?

Rats have 1 pyramid, humans have ~ 12 pyramids


What is a pyramid?

The structure of the pyramid is similar in all species.
Cortex (outer portion) --> outer medulla --> inner medulla --> papilla --> All connected by minor calyces (in humans and other animals that have multiple pyramids) – tubes that collect fluid from apex of pyramids --> major calyces --> renal pelvis

Renal tubules empty at the tip of the pyramids.


Which parts of the kidneys contain smooth muscles and what are their functions?

The walls of the calyces, pelvis and ureter contain smooth muscle. Peristaltic contractions help drive urine into and through the ureter; and may also cause some "reflux" of putative urine over the epithelium that lines the surface of the papilla, where further reabsorption can take place. Such post-nephron modifications of the urine may be important, particularly during diuresis


How many nephrons feed in 1 collecting duct?



In what part of the kidney are the glomeruli located?

Glomeruli are all in the cortex


Which blood goes to the vasorecta?

Blood flow comes in cortex, then small portion goes to vasorecta