urinary system

The kidneys

Filter blood to remove waste (urea creatinine excess ions

Maintain fluid, electrolyte, and acid–base balance.

Produce hormones (erythropoietin → RBC production, renin → blood pressure regulation).

Renal Cortex

The outermost part contains portions of the

functional units called nephrons,

where initial stages of filtration occur.

Renal Medulla

The inner part contains cone-shaped

structures (renal pyramids) that create urine

through reabsorption & secretion.

Renal Pelvis

Funnel Shaped collects urine and channels into ureter

Ureters

Muscular tubes that transport urine from kidneys to bladder vi peristalsis

Urinary bladder

Muscular sac that serves as a reservoir for urine, storing it until the body is ready for its elimination

Urethra

Tube that carries urine from the bladder to the outside of the body during urination

Renal artery

Carries oxygenated blood from the heart (via the aorta) into the kidneys for filtration

Renal Vein

Drains deoxygenated, filtered blood from the

kidneys and returns it to the inferior vena cava.

P-Waste

Pressure control

Water balance

Acid base balance

Salt balance

Toxin removal

Erythropoiesis regulation

Pressure control

Kidneys regulate blood pressure

via the renin–angiotensin–

aldosterone system (RAAS), ADH,

and sodium/water balance.

Water balance

Adjusts water reabsorption in

nephrons; ADH increases water

reabsorption → concentrated

urine, while low ADH → dilute urine.

Acid Base Balance

Maintains blood pH by excreting hydrogen ions (H⁺) and reabsorbing bicarbonate (HCO₃).

Toxin Removal

Eliminates nitrogenous wastes (urea, uric acid, creatinine) along

with drugs and other metabolic byproduct

Erythropoiesis regulation

Kidneys release erythropoietin, stimulating red blood cell production in bone marrow when oxygen is low.

Afferent Arteriole (arrives)

Brings blood into the glomerulus: larger diameter → higher pressure for filtration

Efferent Arteriole (exits)

Carries blood out of the glomerelus smaller diameter → maintains pressure and leads to peritubular capillaries

Bowman’s Capsule/ Glomerulus

What it is: Filtration unit; glomerulus = capillary tuft,

Bowman

’

s capsule surrounds it.

What happens: Filtration of water, ions, glucose, amino

acids, and wastes (urea, creatinine).

Key Point: Large proteins and blood cells stay in the blood

Proximal Convulated Tubule

What it is: First tubule after Bowman’s capsule; lined with

microvilli and aquaporins for massive reabsorption. Reabsorbed: ~65% of water, glucose, amino acids, sodium, chloride, bicarbonate. Secreted: Hydrogen ions (H⁺), ammonia, and some drugs.

Descending thin limb of loop of henle

What it is: Highly permeable to water, but not to solutes.

Reabsorbed: Water (passive osmosis into hypertonic medulla).

Secreted: None.

Ascending loop of henle

What it is: Impermeable to water; permeable to solutes.

Reabsorbed: Sodium, potassium, and chloride are

actively transported out.

Secreted: None.

Distal convulated tubule

What it is: Hormone-sensitive segment.

Reabsorbed: Sodium (via aldosterone),

calcium (via PTH), water (if ADH present).

Secreted: Potassium (K⁺), hydrogen ions (H⁺).

Collecting Duct

What it is: Final urine concentration site; shared by multiple nephrons (hormone controlled)

Reabsorbed: Water (regulated by ADH), urea

(helps medullary gradient).

Secreted: Hydrogen ions (H⁺), potassium (K⁺).

Filtrate

Filtrate is a fluid that has been processed by the glomerulus

through glomerular filtration. It contains water, glucose, amino

acids, urea, & various ions thathave been forced from the blood

into the Bowman's capsule due to pressure. This forms the initial

step of urine production.

Reabsorption

Process that occurs primarily in the

proximal convoluted tubule, loop of

Henle, and distal convoluted tubule

of the nephron, where useful

substances present in the filtrate,

such as water, glucose, and

essential ions, are returned into the

bloodstream. This helps the body to

retain necessary substances and

regulate its fluid balance.

Secretion

Selective transport of certain substances from the blood back

into the tubules of the nephron. Primarily takes place in the distal convoluted tubule and collecting duct. The kidneys excrete

substances like hydrogen ions and potassium ions, thus playing an essential role in maintaining the body's pH balance and electrolyte homeostasis.