Organs of the urinary system
- Kidney: Filter waste products from the blood stream and convert the filtrate into urine
- Ureters: Transport urine from kidney to bladder via peristalsis
- Urinary bladder: Storage of urine
- Urethra: Transports urine from bladder to the outside of the body
The Kidney location
- Located retroperitoneally (posterior to peritoneum)
- Lateral to T12 to L3 vertebrae
- Right kidney lies inferior
- Average size: 12cm, 6 cm, 3cm
- Lateral surface convex, medial is concave
- Renal hilum- where vessels, nerves and ureters enter and leave the kidney
Kidney function
Disposal of waste (toxins, metabolic byproducts, excess water and ions) out of the body in urine while returning needed substances to the blood
- Regulation of blood volume and pressure: filtering role
- Regulation of the blood’s inorganic ion balance- sodium, potassium and phosphate ions (kidneys)
- Acid-base balance through changes in the rates of hydrogen ion and ammonium section
- Regulates of erythrocyte production via erythropoietin
The kidney- protective coverings
Fibrous capsule: Thin tough layer of dense connective tissue adheres to the kidney surface
Perirenal fat capsule: Dense connective tissue, maintains kidney shape, protects from pathogens
Renal fascia: Dense irregular tissue, anchors the kidney to surrounding tissues
Pararenal fat capsule: Fat with adipose tissue: cushioning and insulation
The kidney blood supply
- Kidneys continuously cleanse the blood and thus need a rich blood supply
- 1/4th of systemic output reaches kidneys via renal artery
- Right renal artery is longer than left
- Blood drains via veins into renal vein and then the inferior vena cava
Pathway of blood - Each artery has a paired vein that traces pathway in reverse
- No segmental vein
- Blood from cortical radiate artery then enters arterioles which feed to capillaries
Nephrons
- The main structural and functional unit of the kidney
- Lined with simple epithelium
Composed of: - Renal corpuscle: first part of nephron where filtration occurs
- Renal tubule: long tubular section of proximal tube, loops of henle, distal tubule, collecting duct
Mechanisms of urine formation
- Glomerular filtration: Filtrate of blood leaves kidney capillaries
- Tubular resorption: Most nutrients, water and essential ions reclaimed
- Tubular secretion: Active process of removing undesirable molecules
Nephron renal corpuscle and tubule
Corpuscle
- Has 2 parts:
1. Glomerulus- tuft of capillaries (inner) that are fenestrated (with pores) to allow fluid and small molecules to enter capsular space
Surrounded by the (2) glomerular/ bowman’s capsule
- Produces a filtrate of blood
Tubule
Proximal convoluted tubule:
- Entirely in renal cortex
- Reabsorbs ion, nutrients, plasma proteins, vitamins and water
- Filtrate is called tubular fluid
Bownman’s capsule: filtration (not part of tubule)
Loop of Henle: Reabsorption of ions and water
Distal convoluted tubule:
- Entirely in renal cortex
- Secrets ions into the tubular fluid and reabsorbs water
- Less active in resorption than proximal
Collecting duct
- Each receives urine from several nephrons
- Ducts join to form larger papillary ducts
2 classes of nephrons
Cortical nephrons
- 85% of nephrons
- Short nephron loop
- Glomerulus further from the cortex- medulla junction
- Efferent arteriole supplies peritubular capillaries
Juxtamedullary nephrons
- 15% of nephrons
- Long nephron loop- contribute to kidney’s ability to concentrate urine
- Glomerulus closer to the cortex- medulla junction
- Efferent arteriole supplies vasa recta
Blood vessels associated with nephrons
- Nephrons associate closely with 2 capillary beds:
Glomerulus - Produce filtrate that becomes urine
- Fed and drained by arterioles
- Efferent and afferent glomerular arteriole
- Generate 1 litre of fluid every 8 minutes
- 99% of filtrate is reabsorbed by tubules
Peritubular capillaries in cortical nephrons/ vasa recta in juxtamedullary nephrons - Arise from efferent arterioles draining cortical glomeruli
- Ave adapted for absorption
- Low-pressure, porous capillaries
- All molecules secreted by nephrons into urine are from peritubular capillaries
Urinary tract - ureters
- 25-30 cm long fibromuscular tubes
- Extend from renal pelvis to exist the hilum of the kidney
- Transport urine from kidneys to urinary bladder via peristaltic action of smooth muscle
- Paired, retroperitoneal organs
- Oblique (angled) entry into bladder prevents back flow of urine
Ureters
3 layers, from innermost to outermost:
1. Mucosa
- Transitional epithelium stretchy to the passage of urine
- Distensible transitional epithelium with rugae
- Bundles of primarily smooth muscle fibres surround the mucosa and help propel urine to the outside of the body
2. Muscularis
- 2 smooth muscle layers: inner longitudinal and outer circular
- Peristaltic waves to propel the urine to the bladder
3. Adventitia
- Areolar connective tissue which anchors the ureter to the posterior abdominal region
Urinary bladder
- The urinary bladder is an expandable, muscular reservoir for urine (retroperitoneal)
- Receives blood from branches of the internal iliac arteries
- It is shaped like an upside-down pyramid when empty: when full, it is distended superiorly and oval shaped
Urination innervation
- Process of emptying the bladder via contraction of the detrusor muscle
- Parasympathetic and sympathetic axons of the ANS:
The parasympathetic axons come from the micturition reflex centre located in spinal cord segments S2-24. Stimulate urination - The sympathetic axons comes from the T11-L2 segments of the spinal cord and inhibit innervation
Female urethra
- 3-5 cm long
- Conveys urine from bladder to outside of the body
- Smooth muscle and inner mucosa layer
- Internal urethral sphincter (involuntary) keeps urethra closed when urine is not being passed
- External urethral sphincter (voluntary)- inhibits urination until proper time
- Only transmits urine from bladder to vestibule, an external space immediately internal to the labia minora
Male urethra
- 18-20 cm long passageway from both urine and semen
Prostatic urethra - 2-5cm long
- Extends through the prostate gland where multiple small prostatic ducts enter it
Membranous urethra - 2-5cm long
- Extends from inferior prostrate gland through the urogenital diaphragm
Spongy Ventura - 15cm in erectile tissue in the penis called corpus spongiosum
- Extends to the external urethral orifice
External genitalia
Collectively called the Vulva
Mons Pubis: Skin and subcutaneous connective tissue; overlies the pubic symphysis; pubic hair covers after puberty
Labia Majora: paired, thickened folds of skin, sebaceous glands, connective tissue, homologue of the male scrotum, encloses the labia minora
Labia minora: Paired, highly vascular folds with sebaceous glands and melanocytes
Vestibule: Space between the labia minora; houses opening to urethra and vagina
Clitoris: anterior to vestibule; is erectile tissue
Prepuce: sold of labia minora covering clitoris
Mammary gland
Breasts: Modified sweat glands
Alveoli: increases with pregnancy and produce milk
Lactiferous ducts- drains milk from lobe to sinus
Lactiferous sinuses: expanded enda ducts near nipple; milk
- Storage prior to release from the nipple
Breast milk: Complex sequence of internal/external stimuli
- Prolactin stimulates the production of breast milk
- Oxytocin is responsible for milk ejection
Nipple: raised structure surrounded by an areola containing multiple tiny openings
Suspensory ligaments: Provide support to gland tissue
