Week 1 - Urinary System Flashcards
renal capsule
a thin, tough, and fibrous outer layer that directly surrounds each kidney, composed of DICT (collagen and elastic fibers). it functions to protect the kidney from trauma and infection, while also helping to maintain the kidney’s structural integrity and shape.
adipose capsule
located between the renal capsule and renal fascia, its primarily composed of adipose tissue which provides cushioning by absorbing shock, and insulation to maintain the kidneys at an optimal temperature for their metabolic functions.
renal fascia
a layer of DICT that surrounds the adipose capsule, providing structural support and anchoring the kidneys to surrounding structures like the posterior abdominal wall, to maintain their position in the retroperitoneal space.
ureters
paired tubes that extend from the renal pelvis of each kidney to the posterior aspect of the urinary bladder. they are composed of transitional epithelium, with an underlying lamina propria, a muscularis of smooth muscle (inner longitudinal & outer circular layer), and an adventitia of DICT that anchor the ureters to surrounding structures. their main function is to move urine (through peristalsis) from the kidneys to the urinary bladder.
bladder
the bladder is located in the pelvic cavity, composed of transitional epithelium supported by a lamina propria, a muscularis (detrusor muscle) consisting of an inner longitudinal layer, a middle circular layer, and an outer longitudinal layer. *adventitia around the posterior/inferior surface, and peritoneum around the anterior/superior surface. its main function is to store urine until it is ready to be excreted.
urethra
a tubular structure lined with transitional to stratified squamous epithelium that carries urine from the bladder to the outside of the body, with different lengths in females and males.
transitional epithelium (aka urothelium)
a specialized type of epithelium found in the urinary bladder, ureters, and proximal region of the urethra, allowing these structures to stretch and accommodate changes in volume. it is a stratified type of epithelium, typically with 3-6 layers of cells, held together by tight junctions. the cells appear cuboidal in a relaxed bladder, and squamous-like when the bladder is full.
trigone
a triangular area on the internal surface of the bladder with its apex at the internal urethral orifice, and its base formed by the two ureteric orifices. it serves as a fixed area where the 2 ureteric orifices remain positioned to prevent backflow of urine into the ureters during bladder contraction.
glomerulus
a network of fenestrated capillaries within the renal corpuscle. it is surrounded by a glomerular capsule and serves as the site for filtration of blood.
glomerular capsule (aka Bowman’s capsule)
the structure surrounding the glomerulus, composed of an outer parietal layer (simple squamous epithelium) and an inner visceral layer of podocytes in direct contact with the glomerular capillaries. its function is to collect the filtrate from the glomerulus and direct it into the renal tubules.
filtration membrane
composed of three layers: the fenestrated endothelium of the glomerular capillaries, the basement membrane, and the podocyte slits of the visceral layer of the glomerular capsule. it functions to allow the filtration of small molecules like water, ions, and waste products while preventing larger molecules (e.g., proteins and blood cells) from passing through.
juxtaglomerular apparatus
a specialized structure located where the ascending limb/DCT comes into contact with the afferent arteriole. consists of: juxtaglomerular cells (in the afferent artiole), macula densa cells (in the ascending limb/DCT), and mesangial cells (between the glomerular capillaries). its function is to regulate GFR and blood pressure, primarily through the release of renin.
macula densa
a group of specialized cells located in the DCT/ascending limb where it contacts the afferent arteriole. these cells monitor the NaCl concentration of the filtrate passing through the tubule, and when they detect low NaCl levels they signal the juxtaglomerular cells to release renin, which helps to regulate GFR and BP.
juxtaglomerular cells (aka granular cells)
modified smooth muscle cells located in the afferent arteriole that secrete renin in response to low BP or low sodium levels, which will activate the RAAS to increase BP and GFR.
mesangial cells
specialized cells found within the glomerulus, between the glomerular capillaries. they provide structural support, and have contractile properties that help regulate glomerular filtration and play a role in immune responses by phagocytosing debris.
renin
an enzyme secreted by the juxtaglomerular cells of the afferent arteriole, in response to low BP or low sodium levels in the filtrate. it catalyzes the conversion of the liver protein angiotensinogen into angiotensin I, which is the first step of the RAAS.
aquaporin
integral membrane proteins that form water channels in cell membranes, facilitating the rapid transport of water molecules across cells. crucial for water reabsorption in the nephron.
