Kidneys

Ureters enter the urinary bladder posteroinferiorly.
- This location helps raise the fluid level slowly to avoid crystallization of supersaturated solutions, which could lead to bladder stones.

Fibrous Outer Capsule: Protects the kidneys.
Renal Cortex: Area just beneath the fibrous capsule.
Renal Pyramids: Structures within the renal medulla that resemble pyramids; each terminates at the renal papilla.
- Each renal papilla drains urine into a minor calyx.
Major Calyces: Collect urine from multiple minor calyces and drain into the renal pelvis.
Renal Pelvis: Collects urine before it passes into the ureters.

Renal Arteries: One renal artery per kidney.
- Branch into approximately three segmental arteries.
Segmental Arteries: Give rise to interlobar arteries which run through renal columns.
Interlobar Arteries: Branch into arcuate arteries that rest at the boundary between renal cortex and medulla.
Cortical Radiate Arteries: Also known as interlobular arteries, branch from arcuate arteries and give rise to afferent arterioles.

Afferent Arterioles: Deliver blood to the Bowman's capsule leading to the glomerulus.
Glomerulus: A specialized capillary network where filtration occurs.
- Outgoing blood is carried by efferent arterioles.
- Contains fenestrated capillaries, which allow small substances to be filtered while larger molecules like proteins remain in circulation.

Filtration: Occurs exclusively in the glomerulus; waste and nutrients are pushed out into Bowman’s capsule.
Resorption: Mainly at the proximal convoluted tubule (PCT) and to a lesser extent at the distal convoluted tubule (DCT)
- Most essential nutrients (e.g., glucose, amino acids) are resorbed in the PCT.
Secretion: Movement of substances from the blood to the filtrate, occurs at both PCT and DCT.
Excretion: Resulting urine leaves the nephron at the collecting duct.

Descending Limb: Permeable only to water; aids in concentrating urine.
Ascending Limb: Thick segment, impermeable to water, allows sodium, potassium, and chloride ions to be actively transported out.

Aldosterone: Increases sodium reabsorption in the DCT; leads to water retention.
Antidiuretic Hormone (ADH): Promotes water reabsorption primarily in the collecting duct.
Atrial Natriuretic Peptide (ANP): Released when blood volume is high; inhibits sodium reabsorption, promoting diuresis.

High blood pressure (hypertension) can lead to kidney damage due to excessive filtration and loss of useful substances.
Kidneys autoregulate by constricting afferent arterioles to lower pressure and ensure adequate filtration.
Low blood pressure (hypotension): Efferent arterioles are constricted to increase glomerular pressure and filtration rate.

Distal Convoluted Tubule (DCT): Involved in fine-tuning through resorption and secretion, influenced by hormonal factors (e.g., aldosterone for sodium).
Collecting Duct: Contains principal cells responsive to ADH and intercalated cells responsible for acid-base balance.

SGLT2: Sodium-glucose cotransporter located in the PCT; responsible for glucose reabsorption.
- If serum glucose exceeds the reabsorptive capacity, glucose spills into urine (glucosuria) leading to polyuria, polydipsia, and polyphagia.
Elevated glucose causes osmotic diuresis, increasing urine volume and the risk of dehydration.