BISC 101 Week 7 Lecture 2

General principle to maximize rate of transfer

Rate of transfer equation: Fick’s law

1. Area for exchange

2. partial pressure concentration difference

3. Distance (Thickness of barrier to diffusion)

Goose Homeostasis: hot weather

Goose homeostasis: cold weather

Osmotic regulation: Salmon in salt water

Osmotic regulation: Salmon in freshwater

NaCl(Salt) excretion

Overall goal: Release Na+ and Cl- from body

Salt excretion step 1

• Sodium potassium pump. Sodium moves into blood/ECF, potassium moves into epithelial cells.

• Uses ATP.

• Primary active transport.

• Purpose: establish sodium concentration gradient for steps 2 and 4. (High in blood, low in cell)

Salt excretion step 2

• Sodium, chloride, and potassium transported from blood/ECF into epithelial cells.

• Uses concentration gradient of Sodium. Secondary active transport.

• Purpose: brings chloride into the cell, establishing concentration gradient for step 3.

Salt excretion step 3

• Chloride moves outside of cells into the ocean. Potassium moves into blood from cells.

• Doesn’t use energy. Passive (Facilitated diffusion)

• Purpose: excrete Chloride, rebalance potassium into blood

Salt excretion step 4

• Sodium diffuses from blood to the ocean, between cells.

• Doesn’t use energy. Simple Passive transport.

• Purpose: To excrete sodium.

Kidneys

• Where osmoregulation occurs in terrestial vertebrates

• Renal artery: brings blood (with nitrogenous wastes) into kidneys

• Renal vein: carries blood away

Renal corpuscle

• where filtration occurs

• blood enters renal corpuscle and filtration occurs as it passes through.

• proteins, cells, and large components of blood are too big to fit through the pores.

• fluid is now pre-urine once filtered

Proximal Tubule

• Reabsorption of small molecules

• Filtrate contains water and small solutes (e.g., urea, glucose, amino acids, vitamins, electrolytes)

• Almost all nutrients (& most of the NaCl and water filtered by renal corpuscle) are reabsorbed here.

Loop of Henle descending

Water reabsorbed (aquaporins), using salt gradient

Loop of Henle ascending

Na+ and Cl- reabsorbed, using and making salt gradient

active Na & Cl transport in ascending limb makes the medulla hypertonic, which drives the water transport in the descending limb.

impermeable to water

Distal Tubule

Reabsorption continues

• If Na+ is low in blood, it can be reabsorbed (K+ and H+ from blood may move into distal tubule) – Hormone: Aldosterone

• The filtrate that enters the distal tubule is always dilute

Collecting Duct

Water reabsorption, especially if dehydrated

• Antidiuretic hormone (ADH) plays a role in the production of concentrated or dilute urine

• ADH: part of a negative feedback loop, returning the system to a set point.