Homeostasis & The Kidney

Homeostasis

The maintenance of a constant environment

What does the internal environment include

tissue fluids that bathe cells: supplying nutrients, removing wastes, maintaining glucose concentration, pH, core temperature and solute potential

What system controls homeostatic responses

the endocrine system

Negative feedback system

An output from an effector reduces the effect of a stimulus and restores the system to its original level

Positive feedback system

An effector increases a change which moves the system further from the original level

Example of a negative feedback system

Glucose concentration in the plasma. If glucose concentration increases above the set point, insulin is secreted, reducing the glucose concentration by converting it to glycogen and increasing the rate at which it is respired. If the levels fall below the set point, glucagon is secreted, which results in glycogen being converted to glucose.

Example of a positive feedback system

Oxytocin stimulates the contraction of the uterus at the end of a pregnancy. The contractions stimulate the production of more oxytocin, which increases the stimulus (the uterine contractions).

Excretion

The removal of wastes made by the body

What are the 4 excretory organs in mammalian bodies

The lungs, kidneys, skin and liver

2 main functions of the Kidney

Excretion and osmoregulation

Deamination word equation

Amino acid —> a-keto acid + ammonia —> urea

Nephron

An individual blood-filtering unit.

Glomerular filtration rate

The rate at which fluid passes from the blood into the glomerular capillaries into the Bowman’s capsule

Selective reabsorption

The process by which useful products are reabsorbed back into the blood, as the filtrate flows through the nephron

How much salt is reabsorbed to the blood from the glomerular filtrate and how

70% by mostly active transport

How much glucose and amino acids is reabsorbed to the blood from the glomerular filtrate and how

All, by co-transport with sodium ions

How much water is reabsorbed to the blood from the glomerular filtrate and how

90%, by osmosis

How much urea/small proteins is reabsorbed to the blood from the glomerular filtrate and how

50%, by diffusion