BIO 225 - Osmoregulation

Diadromus fish

Fish which migrate between saltwater and freshwater

Catadromus fish

Live in freshwater but migrate to saltwater to spawn

• Eels

Anadromus

Live in saltwater but migrate to freshwater to spawn

• Salmon

Migration and Ion Transport Functions of Epithelia

Ion transport functions of epithelia must change during migration

• Managed by hormones

• Salt vs. freshwater epithelia

Corneocyte and Stratum Corneum

Cells which prevent the evaporation of water in desert animals

• Extra layer on the normal (human) integumentary system

Water Conservation - Land Animals

Cover external surfaces with a layer of hydrophobic molecules

• Mucus

• Cornified stratum corneum with Keratin

• Cuticle with chitin

Sources of Water for Terrestial Animals

1. Dietary water: Eating

2. Metabolic water: Generated through digestion

3. Drinking

6 Functions for the Kidney

1. Excretion of Metabolic wastes and toxins

2. Ion Balance

3. Osmostic Pressure

4. Blood Pressure

5. pH Balance

6. Hormone Production

Nephron and it’s 2 parts

Functional unit of the kidney

• Renal Tubule

• Vasculature

Renal Tubule

Lined with transport epithelium

• Has various segments with

Nephron Vasculature

Capillary beds surrounding renal tubule

Cortical Nephron

Smaller Loop of Henle

• Limited capacity to generate concentrated urine

Juxtamedullary Nephron

Long Loop of Henle

• Large capacity for concentrated urine

Vasa Recta

Countercurrent crossed system of blood vessels of the nephron

Glomerular Filtration Rate - GFR

Amount of filtrate produced per minute

GFR Influences

1. Glomerular capillary hydrostatic pressure

2. Bowman’s capsule hydrostatic pressure

3. Oncotic pressure

Oncotic Pressure

Osmotic pressure due to protein concentration in the blood

Intrinsic Regulators of GFR

Change the rate of filtration

1. Mesangial Control

2. Myogenic Regulation

3. Tubuloglomerular Feedback

Mesangial Control

Alters glomerulus permeability

Myogenic Regulation

Constriction/dilation of afferent artery

Tubuloglomerular Feedback

Paracrine signalling via the macula densa cells and the juxtaglomerular cells, controlling the afferent artery diameter

Primary Urine

Initial filtrate filtered in the Bowman’s Capsule that is isosmotic to the blood

• Most of the water and salt is reabsorbed using transport proteins and energy, but the rate of reabsorption is limited by number of transporters

Renal Threshold

Blood concentration of a specific solute at which the kidneys stop fully reabsorbing it, causing leakage into the urine

• Reabsorption can’t go on forever

Proximal Tubule

Where most solute and water reabsorption occurs

• Solutes typically use the Na+ Cotransport

• Water follows by osmosis

Undergoes transcellular and paracellular transport

Reabsorption of Glucose

Secondary Active Transport

• Na/H and Na/K pumps build gradient, then glucose is transported via the Na/Glucose cotransporter

Molecules Secreted (blood to filtrate)

K+, NH4+, H+, pharmaceuticals, water-soluble vitamins

• Requires transport proteins and energy

Medulla Osmolarity

Deeper into the medulla you go, the higher the osmolarity (more concentrated)

Distal Tubule

Reabsorbs salts and water; can secrete K+

Transport controlled by hormones: Parathyroid Hormone and Aldosterone

Parathyroid Hormone

Increases Ca2+ reabsorption

Aldosterone

Increases K+ secretion

Juxtaglomerular Cells and Renin (enzyme) Secretion

1. Baroreceptors

2. Sympathetic Neurons

3. Macula Densa cells

Released when blood pressure or GFR is low

Angiotensinogen 2

Steroid hormone which targets cells in the distal tubule and collecting duct

• Stimulates sodium and water reabsorption from urine

• Enhanced K+ excretion

• Stimulated also by increase in circulating K+