7/19 & 7/22: Osmoregulation

What is osmoregulation?

Maintaining osmotic balance across different compartments/membranes

Why is osmoregulation important?

Water and electrolytes are constantly being introduced (food) and removed (excretion) from the body. Osmoregulation is necessary for maintaining ideal ion concentrations/osmotic balance (otherwise toxic waste may accumulate)

What are the three major fluid compartments in mammals?

Blood plasma, extracellular fluid, and interstitial fluid

What is concentration?

General term for an amount of substance in a given volume

Out of osmolarity, molarity, osmolality, and molality, which ones measure the volume of the solvent?

Osmolarity and molarity

Out of osmolarity, molarity, osmolality, and molality, which ones measure the mass of the solvent?

Osmolality and molality

What is the functional unit of the kidney?

Nephron

What are the two types of nephrons?

Cortical and juxtamedullary

What are the three general parts of the nephron?

Renal corpuscle, renal tubule, and associated capillary network

What does the renal corpuscle consist of?

Glomerulus and Bowman's capsule

What does the renal tubule consist of?

Proximal convoluted tubule, loop of henle, distal convoluted tubule

What does the associated capillary network of the nephron consist of?

Afferent and efferent arterioles, peritubular capillary network, and vasa recta

What is the vasa recta?

Long capillaries parallel to the loop of Henle (Rect = Straight, Vasa = Vessels.)

Which nephrons have vasa recta?

Juxtamedullary nephrons

Which parts of the nephron are in the cortex?

Glomerulus/Bowman's capsule, proximal and distal convoluted tubules

Which parts of the nephron are in the medulla?

Loop of Henle and collecting duct

Which parts of the nephron contain blood?

Afferent arteriole, glomerulus, efferent arteriole, peritubular capillaries, and vasa recta (if present)

Which parts of the nephron contain filtrate?

Glomerulus, PCT, loop of henle, DCT, and collecting duct

What are the different processes involved in the nephron?

Glomerular filtration, secretion, reabsorption, and excretion by urine

Which parts of the nephron carries out secretion?

DCT

Which parts of the nephron carries out reabsorption?

PCT mainly, also loop of Henle, DCT, and collecting ducts

Does reabsorption involve passive or active diffusion?

Both, but mostly active

Which processes in the nephron involve only passive movement?

Filtration and excretion

What is the formula comparing all of the processes in the nephron?

Excreted = Filtered + Secreted - Reabsorbed

How can I tell if an animal is an osmoconformer or osmoregulator?

1. If body fluid OC differs from EnvOC, it is an osmoregulator.

2. If BFOC = EnvOC, you need to change the EnvOC. If BFOC changes very similarly alongside it (i.e. matches the isosmotic line), the animal is an osmoconformer.

What are contractile vacuoles?

Vesicles formed from the cell membrane to induce endocytosis and subsequent exocytosis- can be representative of kidneys in humans as they regulate similar things

Which animals have contractile vacuoles?

Sponges, hydra

What are nephridia?

Excretory organs that filter and allow tubular reabsorption by a capillary system

Which animals have nephridia?

Earthworms

What are Malpighian tubules?

Excretory structures lined with microvilli to perform absorption and maintenance of osmotic balance

Which animals have Malpighian tubules?

Insects and other anthropods

What is the blood osmolarity set point in humans?

300 mOsm

What is the only regulated blood variable that the ANS controls?

Blood pressure

How does parasympathetic stimulation affect heart rate?

Hyperpolarizes the SA nodes, which results in slower depolarization and thus a slower heart rate

How does sympathetic stimulation affect heart rate?

Depolarizes the SA nodes, which results in faster depolarization and a faster heart rate

The SA node primarily controls:

Heart rate

Ventricular muscles primarily controls:

Stroke volume

Vessels primarily regulate:

Total peripheral resistance

What brain centers are activated during periods of increased blood pressure?

Cardiac inhibitor centers

What brain centers are activated during periods of decreased blood pressure?

Cardiac accelerator centers and vasomotor center

What are some whole body effects of the RAAS system?

Increased blood volume, blood pressure, Na+ concentration, and decrease in blood osmolarity

What is the regulatory step in the RAAS system?

Renin converting angiotensinogen to angiotensin-1

What stimulates the release of renin?

Decreased blood pressure or blood volume

What is angiotensinogen produced by?

Liver

What is renin produced by?

Kidney

What is ACE produced by?

Lungs

What is ADH produced by?

Posterior pituitary

What is aldosterone produced by?

Adrenal gland

What are some steps in the RAAS pathway that are NOT regulated?

Angiotensinogen production and ACE

What is the "active" hormone between angiotensinogen, angiotensin I, and angiotensin II?

Angiotensin II

What are some direct effects that angiotensin II has?

Increases the feeling of thirst, decreases filtration rate, vasoconstriction and increases in cardiac output (all working to increase volume and MAP)

What hormones are stimulated by angiotensin II?

ADH and aldosterone/vasopressin

Out of the entire RAAS pathway, which hormone is a neurohormone?

ADH (it is produced by the posterior pituitary)

What are the effects of ADH?

Increased Na+ and water reabsorption, vasoconstriction

What are the effects of aldosterone?

Increased Na+ and water reabsorption (resulting in increased blood volume)

What is ANP produced by?

Endocrine cells in the atrium

What stimulates the release of ANP?

Increased volume (which can be sensed through stretch receptors)

What are the effects of ANP?

Decrease blood pressure, blood volume, Na+ concentration and increase in blood osmolarity (essentially the EXACT opposite of RAAS system)

Do the RAAS and ANP systems affect all processes in the kidney (filtration, secretion, reabsorption, and excretion)?

NO, they do not affect secretion directly

What are the general conclusions of the Sakamoto paper?

Organisms are weak osmoregulators. They are ionoregulators and utilize octopressin to regulate BFOC