Excretory System

role of the large intestine in excretion

removes the toxic or indigestible substances that result from digestion, forming feces

role of the liver in excretion

breaks down alcohol and heavy metals into less toxic forms which are then removed by the kidneys through urine

Why must excess amino acids be broken down in the liver?

cannot be stored in our body

will lead to toxic nitrogen buildup

deamination

chemical reaction in the liver that breaks down the amino acid to remove the nitrogen-containing amine group

prevents the buildup of ammonia that contains the toxic nitrogen

How is ammonia (NH₃) made safe for excretion?

converted into urea (waste product) in the liver

then transported to the kidneys to be filtered out and excreted in urine

What happens to the keto acid produced during deamination?

used for energy in liver cells, aerobic (oxygen) respiration, or converted into glucose or fat

kidneys function

filter wastes from the blood and excrete it in urine

usually excretes urea

What system are the kidneys part of?

urinary/excretory system

components of the excretory system

2 kidneys

2 ureters

bladder

urethra

renal vein

renal artery

main function of the excretory system

filter blood and remove waste by excreting urine

ureters

carry urine to the bladder

bladder

Hollow sac that collects and stores urine

urinary sphincter

valve at the base of the bladder that controls urine release

stretch receptors

sensory nerve endings on neurons that detect the stretching of tissues or organs

ex. When the bladder fills with urine and stretches, receptors sends a signal to the brain to release it

urethra

tubule that carries urine from the bladder out of the body

three main functions of the kidneys

Remove waste (urea and uric acid), balance blood pH, and maintain water balance

three main layers of the kidney

Renal cortex, medulla, and renal pelvis

renal cortex

outer layer of the kidney

filtering layer that contains the upper portion of nephrons and connective tissue

medulla

middle layer

collecting layer that contains renal pyramids and lower portions of nephrons

renal pelvis

centre of the kidney

draining layer made up of vessels that connect the kidney to the ureter

renal artery

carries blood into the kidney

renal vein

carries filtered blood out of the kidney

nephrons

functional units of the kidney

long tubule with a series of associated blood vessels where filtration and reabsorption occur

where are nephrons found in the kidneys

cortex (outer layer) and the medulla (middle layer)

parts of the nephron

Glomerulus

Bowman’s capsule

Proximal convoluted tubule

Loop of Henle

Distal convoluted tubule

Collecting duct

glomerulus

high-pressure capillary bed

the site of filtration in the nephron

Bowman’s capsule

cup-like structure that surrounds the glomerulus and catches the filtrate

Why is there high pressure in the glomerulus?

afferent arteriole has a larger diameter than the efferent arteriole, more blood can come in than exit

causing a backup of blood and increased pressure

What substances are filtered from the glomerulus into Bowman’s capsule?

Water, urea, uric acid, and salts

small enough to pass through the filter and enter the bowman’s capsule

Where does filtrate go after passing through the Bowman’s capsule?

Into the nephron tubule

peritubular capillaries

network of capillaries that surround the nephron

After filtration, not everything in the filtrate should be lost in urine so it reabsorb nutrients from the filtrate

4 stages of urine formation

1. glomerular filtration

2. tubular reabsorption

3. tubular secretion

4. water reabsorption

What happens during glomerular filtration?

Blood pressure forces water, urea, salts and other small solutes from the blood that’s in the glomerulus into the Bowman's capsule

Why are glomerular capillaries good for filtration?

porous (tiny holes) and permeable to small solutes

wont let big substances pass through

How does blood pressure in the glomerulus compare to other parts of the body?

about four times greater, which acts as the force for filtration

Is glomerular filtration selective?

it is non-selective, any solute small enough will filter through

pathway of the filtrate

bowman’s capsule - proximal tubule - loop of henle - distal tube - collecting duct

Where does most tubular reabsorption occur?

proximal tubule and Loop of Henle

how is filtrate reabsorbed back into the body

active (energy needed) and passive (no energy needed) are used to reabsorb essential solutes back into the blood

how does active transport reabsorb in the proximal tubule

Cells with many mitochondria use active transport (with ATP) to move sodium, glucose, K⁺, and amino acids back into the blood

how does negative ions get reabsorb in the proximal tubule

follow passively due to charge attraction

how does osmosis reabsorb in the proximal tubule

Water follows because of the higher solute concentration in the blood than the proximal tube