Excretory System

Nitrogenous waste is usually converted to what?

Ammonia (later converted into urea in humans)

(Note: excretion handling differs between organisms)

Where are the places in the human body where excretion takes place?

lungs, liver, skin, kidneys

What is the overview of excretion in the lungs?

CO2 and H20 (gases) diffuse from blood and are continually exhaled.

What is the overview of excretion in the liver?

processes:

- nitrogenous waste

- blood pigment wastes

- other chemicals

produces:

- urea

What is the overview of excretion in the skin?

sweat glands in skin secrete H20 and dissolved salts, regulating body temperature.

(Note: skin is largest organ. sweat gland function decreases as we age)

What is the overview of excretion in the kidneys?

takes in blood, filters and excretes substances based off homeostatic needs.

What are the three regions of the kidney?

1. outer cortex

2. inner medulla

3. renal pelvis (drains to ureter)

What is the path of waste when it reaches the kidney?

kidney -> ureter -> bladder -> urethra

When blood pressure is too high or too low, what organ directly functions to adjust accordingly?

kidney

What is the functional unit of the kidney?

nephron

What are the components of the renal corpuscle?

1. Glomerulus

2. Bowman's capsule

What household item does the glomerulus act like?

sieve - strains out unwanted materials

What are the two important arterioles associated with Bowman's capsule?

1. afferent arteriole (in)

2. efferent arteriole (out)

How does plasma transfer to the Bowman's capsule?

hydrostatic pressure forces plasma through fenestrations. screens out large plasma proteins

(this pressure can be adjusted based on the body's needs- such as blood pressure regulation)

what is the substance that gets into the Bowman's capsule called?

filtrate/primary urine

What are cells in Bowman's capsule that filter blood and hold back large molecules and allow smaller molecules to get through?

podocytes

When the efferent arteriole passes back out of the glomerulus, where does it go?

webs around the entire nephron structure forming peritubular capillaries and vasa recta. Eventually, it joins the renal branch of the renal vein.

What is the function of the peritubular capillaries?

surround proximal convoluted tubule and distal convoluted tubule and reabsorb materials

What is the function of the vasa recta?

surrounds the Loop of Henle/maintains concentration gradient

When substances are reabsorbed from the tubules (or secreted into them), where does it takes place?

interstitium

(Note: network of capillaries that lets us reabsorb into/secrete from the blood)

What are the componenets of the renal tubule?

1. proximal convoluted tubule

2. loop of Henle

3. distal convoluted tubule

4. collecting duct

(Note: the renal tubule as a whole is the 2nd part of the nephron)

Active reabsorption of what substances take place in the proximal convoluted tubule (PCT)?

almost all glucose, amino acids, and some NaCl

Passive reabsorption of what substances begins in the PCT?

K+ and HCO3-

Why is the renal cortex not salty?

water follows ions out of the PCT

What get secreted into the filtrate in the PCT?

drugs, toxins, NH3, and H+ ions (by anti-port with Na+)

What is the net result of the PCT

- reduce amount of filtrate

- keep concentration the same

Due to a large amount of active reabsorption in the PCT cells, they will have a lot of which organelle inside their cells?

mitochondria

What structure makes up the majority of the nephron?

Loop of Henle

To what substance is the descending loop only permeable to?

water (via lots of aquaporins)

How does the medulla stay salty if the descending loop is permeable to water?

the water is picked up by the vasa recta, keeping the medulla salty

What happens to the solute concentration in the descending loop of Henle?

it increases

What substance is the ascending loop permeable to?

solutes (NaCl)

What substance is the ascending loop impermeable to?

water

How does the medulla grow salty at the ascending loop?

first passively, then actively by pumping out NaCl

What happens to solute concentration in the ascending loop?

it decreases

Why isn't the cortex salty at the distal convoluted tubule (DCT)?

glucose, ions, and water get reabsorbed (makes the cortex not salty)?

What ions of the filtrate get actively pulled out and reabsorbed in the DCT?

NaCl and HCO3-

What ions are actively secreted into the DCT?

K+ and H+

What happens to water in the DCT?

passively pulled out

What happens to the filtrate concentration in the DCT?

overall, it is lowered (even though some water passively moves out)

What hormones can act on the end of the DCT to increase its permeability to water, which is normally not permeable?

Aldosterone, and to a lesser extend ADH

What is the function of the collecting duct?

- collects the remaining filtrate

- functions are highly dependent on what hormones are acting on it

What can happen to NaCl in the upper medulla portion of the collecting duct?

resorption

How permeable is the collecting duct to water?

not permeable, unless ADH acts on it

Why is urea resorbed at the collecting duct?

maintain the medulla's osmolarity (can re-enter the loop of henle - called urea recycling)

What are the two hormones that can change the concentration of urine in the collecting duct?

ADH and aldosterone

how does ADH (vasopressin) act in the kidneys?

increased aquaporins (because of concentrated medulla, water wants to leave the tubule)

how does aldosterone act?

- increases Na+/K+ anti-port

- water follows Na+ ions out

Why does alcohol increase urine output?

alcohol blocks the creation of ADH (vasopressin), so less resorption of H20

What are the 4 steps of urine formation?

1. Filtration

2. Reabsorption

3. Secretion

4. Excretion

Of what does the filtration step of urine formation consist?

fluid passes through glomerulus (passive process driven by hydrostatic pressure of blood)

Of what does the reabsorption step of urine formation consist?

glucose, salts, and amino acids are reabsorbed from the filtrate and return to the blood

Where does the majority of reabsorption take place?

PCT via active transport

What is the only passive transport in the reabsorption process?

movement of water and the leaving of bicarbonate

Of what does the secretion step of urine formation consist?

substances go from the peritubular capillaries into the nephron (both passive and active transport)

What is the overall path of the excretory system?

- renal corpuscle

- proximal convoluted tubule

- descending loop of Henle

- ascending loop of Henle

- distal convoluted tubule

- collecting duct

- renal calyx

- ureter

- urinary bladder

- urethra

What is the macula densa?

area of closely packed specialized cells lining the DCT

What does the juxtaglomerular apparatus do if the blood pressure is too low?

granular cells —> secrete renin —> angiotensin cascade —> tells adrenal cortex to synthesize aldosterone —> more water is reabsorbed from the DCT —> blood pressure rises

What is the end goal of the juxtaglomerular apparatus?

regulate blood pressure (by monitoring filtrate pressure of the DCT)

What is created by the entering and exiting of solutes, and increases from the cortex to the medulla?

osmolarity gradient

What term describes the fact that the descending loop is permeable to water and the ascending loop is permeable to salts and ions, the medulla is very salty and facilitates water reabsorption.

counter current multiplier

The innervations of the sympathetic nervous system primarily affect what?

afferent arterioles (constrict it —> reduces urine output)

For humans, how much fluid is filtered and reclaimed, and how much is excreted per day?

~180 liters is filtered and reclaimed

and 1-2 L are excreted per day

TERM

Bowman's Capsule

LOCATION

TERM

proximal convoluted tubule

LOCATION

TERM

descending loop of Henle

LOCATION

TERM

Loop of Henle

LOCATION

TERM

distal convoluted tubule

LOCATION

TERM

collection duct

LOCATION

TERM

ascending loop of Henle

LOCATION