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Yr 3 Sem 1 > Week 6 > Flashcards

Week 6 Flashcards

1
Q

What is the urinary system made up of?

A

kidneys, ureters, bladder & urethra.

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2
Q

What is the upper urinary tract made up of?

A

Kidneys & Ureters

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3
Q

What is the lower urinary tract made up of?

A

Bladder & urethra

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4
Q

What are the functions of the kidney? (2)

A

URINE FORMATION
Filter ~1,200 mL of blood/minute

Regulates levels of fluids and electrolytes
Removes metabolic wastes, drugs and toxins

Maintains acid-base balance: H+, HCO3-

ENDOCRINE & METABOLIC FUNCTIONS
Erythropoietin: blood cell production

Renin: blood pressure regulation

Vitamin D: converts inactive form (cholecalciferol) to active form (calcitriol)

Gluconeogenesis: formation of glucose from non-carbohydrate sources

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5
Q

What are the kidneys?

A

Paired, bean-shaped structures
Reddish-brown colour

10cm (l) x 5cm (w) x 2.5 cm (d)
~130g in weight

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6
Q

What is the gross external structure of the kidneys? (2)

A

Kidney poles & surfaces:
Lateral border - convex
Medial border - concave, has a vertical cleft (renal hilum) which extends into an internal cavity (renal sinus)

Structures entering hilum: (ant. to post.)
Renal vein
Renal artery accompanied by autonomic nerves and capsular lymphatics
Renal pelvis (funnel-shaped beginning of the ureter)

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7
Q

What are the supporting tissues of the kidneys? (3)

A

Surrounding each kidney (superficial to deep):

Renal fascia
Anchors the kidney and adrenal gland to surrounding structures

Perinephric fat
Variable amount
Cushions the kidney
Helps retain its position

Fibrous capsule
Strong, transparent sheath composed chiefly by collagen & elastin

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8
Q

What is the location of the kidneys?

A

Kidneys extend approximately from T12 to L3
Lie obliquely in the paravertebral gutters

Rt kidney is crowned by the liver and sits lower than the Lt
Rib 12 overlies the upper pole of Rt kidney

Rib 11 overlies the upper pole of Lt kidney

Vertical range of movement: ~2cm (during full respiratory excursion of the diaphragm)

Retroperitoneal: the kidneys lie on the posterior abdominal wall (anterior aspect covered by parietal peritoneum)

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9
Q

What is the gross internal structure of the kidneys? (3)

A

CORTEX
Lies beneath the capsule

MEDULLA
Arranged as pyramids (cone-shaped masses), that have a papilla and base
Pyramids: striped appearance due parallel bundles of urine collecting tubules

Renal columns: inward extensions of cortical tissue that separate the pyramids
Pyramid + surrounding cortical tissue = kidney lobe (~8 per kidney)

RENAL PELVIS
Urine drains from the papillae of the renal pyramids into several minor calyces
Minor calyces converge to form 2-3 major calyces

Major calyces empty into the renal pelvis
A funnel-shaped expansion continuous with the ureter leaving the hilum

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10
Q

What is the arterial supply to the kidneys?

A

Renal arteries

Arise from aorta at the level of L1/2 IVD
Rt renal a. slightly longer than Lt

Upon entering the renal sinus, each artery divides into smaller branches:

Segmental aa –>interlobar aa –>arcuate aa –>cortical radiate aa –>afferent arterioles –>glomerular capillaries

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11
Q

What is the venous drainage of the kidneys?

A

Renal veins

Each renal vein is formed by 5-6 interlobar veins that unite at the hilum

Lt renal v. is longer than Rt
Runs over ant. surface of aorta to the IVC

Lt renal v. is joined by the Lt suprarenal v. & Lt gonadal v. before draining into the IVC

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12
Q

What is the lymphatic drainage of the kidneys?

A

Para-aortic nodes near the origin of the renal arteries

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13
Q

What is the nerve supply of the kidneys?

A

Parasympathetic: CN X Vagus
Sympathetic: T10 - 12 splanchnic nn
Visceral afferents

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14
Q

What is the basic functional unit of the kidneys?

A

Nephron

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15
Q

What is the function of a nephron?

A

Blood filtration and urine formation

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16
Q

What are the key components of the microscopic structure of the kidney? (2)

A

Renal corpuscle

Glomerulus
Glomerular (Bowman’s) capsule

Renal tubule & collecting duct

Proximal convoluted tubule
Nephron loop (loop of Henle)
Distal convoluted tubule
Collecting duct

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17
Q

What is the glomerulus?

A

A ‘knot’ of capillaries
Receives blood from an afferent arteriole and drained by an efferent arteriole

Fenestrations (capillary pores) allow for the easy formation of filtrate

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18
Q

What is the Glomerular (Bowman’s) capsule?

A

A cup-shaped hollow structure that surrounds the glomerulus, continuous with the renal tubule

Features podocytes (specialised epithelial cells with foot processes) that cling to the capillaries
Foot processes of podocytes contain filtration slits
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19
Q

What is the renal tubule composed of? (3)

A

~3cm in length

PROXIMAL CONVOLUTED TUBULE
Receives filtrate from Bowman’s capsule

Cuboidal cells lining the wall of PCT possess microvilli & abundant mitochondria
Large capacity for the reabsorption of substances

LOOP OF HENLE
Descending limb – squamous cells (THIN segment)
Ascending limb – cuboidal/columnar cells (THICK segment)

DISTAL CONVOLUTED TUBULE
Cuboidal cells lack microvilli
Conveys urine to the collecting ducts

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20
Q

What is the collecting duct?

A

Each collecting duct receives filtrate from many nephrons

Collecting ducts give the pyramids their striated appearance

Passage through the medulla allows for final adjustments to urine concentration & content

The ducts fuse together and deliver urine to the minor calyces via the renal papilla

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21
Q

What are the types of nephrons? (2)

A

Cortical

Juxtamedullary

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22
Q

What is a cortical nephron?

A

85% of nephrons
Located predominantly in the cortex

Efferent arterioles of cortical nephrons feed into a network of peritubular capillaries that cling to adjacent renal tubules

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23
Q

What is a juxtamedullary nephron?

A

Originate close to the cortex-medulla junction
Posses long nephron loops that extend deep into the medulla

These nephrons create an osmotic gradient in the medulla that allows the kidneys to create concentrated urine (more on this later!)

Efferent arterioles of juxtaglomerular nephrons feed into vasa recta – long bundles of vessels

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24
Q

What is the juxtaglomerular apparatus (complex)?

A

A region where the most distal portion of the loop of Henle lies against the afferent (and sometimes efferent) arteriole of its glomerulus

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25
What are the specialised cells of the juxtaglomerular apparatus (complex)? (3)
Macula densa cells Located in the wall of the tubule, act as chemoreceptors Monitor the NaCl content of filtrate entering the DCT Juxtaglomerular cells Located in the arteriolar walls, act as mechanoreceptors Contains granules of renin Extraglomerular mesangial cells Lie in between the tubule & arteriole Help to regulate MD & JG cells
26
What is urine composed of?
95% water and 5% solutes ``` Normal solutes (in order of decreasing concentration): Urea, Na+, K+, PO43-, SO42-, creatinine, uric acid ``` Variable amounts: Ca2+, Mg2+, HCO3- ``` NITROGENOUS WASTES Urea (breakdown of amino acids) Uric acid (breakdown of nucleic acids) ```
27
What are some abnormal urinary constituents?
blood proteins, WBCs (pus), bile pigments, glucose, ketones
28
What are the major processes of urine formation? (3)
Involves three major processes: GLOMERULAR FILTRATION Occurs in the renal corpuscle Produces a cell-free and protein-free filtrate TUBULAR REABSORPTION Selective reabsorption of substances that the body needs to keep Healthy kidneys: 99% of water & salt; all glucose, amino acids Anything that is not reabsorbed becomes urine Each day: ~180L of filtrate is formed, but only ~1.5L leaves the body as urine TUBULAR SECRETION Selective addition of substances from blood into the filtrate
29
What is filtrate formation?
a passive process that relies on net outwards pressure from the glomerular capillaries into the capsular space
30
What are the filtration membrane components?
Endothelium of glomerular capillaries (fenestrated) Podocytes of Bowman’s capsule (foot processes have filtration slits) Basement membrane Filtration membrane permits passage of molecules < 3nm in diameter Water, electrolytes, glucose, amino acids, nitrogenous wastes
31
What is the glomerular filtration rate (GFR)?
volume of filtrate formed each minute by the kidneys
32
What are factors affecting GFR? (3)
NET FILTRATION PRESSURE (NFP) Key determinant of NFP is the hydrostatic pressure of the glomerular capillaries (HPGC) HPGC is the main controllable factor in the body Most homeostatic mechanisms act on this one variable – usually by altering blood volume or changing the diameter of the afferent arteriole TOTAL SURFACE AREA AVAILABLE* FILTRATION MEMBRANE PERMEABILITY* *These two factors can be impacted by disease states
33
What is normal GFR?
180L of filtrate per day ~ GFR of 120-125mL/min ``` Clinically, GFR is estimated by an equation that takes into factors including age, sex and serum creatinine Estimated GFR (eGFR) ``` Normal GFR: >90 mL/min Mild loss of kidney function: 60-89 mL/min Kidney failure: <15mL/min
34
What are consequences of inadequate GFR?
Excess fluid, solutes, waste
35
How does the body maintain GFR?
Body possesses intrinsic and extrinsic mechanisms that maintain GFR
36
What is the intrinsic regulation of GFR? (3)
Autoregulation: maintenance of GFR due to mechanisms local to the kidney Myogenic mechanism Vascular smooth m. contracts when placed on stretch (and relaxes when not) High systemic BP: afferent arterioles constrict to limit NFP and prevent glomerular damage Low systemic BP: afferent arterioles dilate Tubuloglomerular mechanism Initiated by macula densa cells (chemoreceptors sensitive to NaCl concentration of filtrate) High GFR: not enough time for reabsorption of NaCl from filtrate MD cells detect the high NaCl and release adenosine (induces vasoconstriction of afferent arterioles) ``` Prostaglandin E2 (PGE2) Produced by renal cells (tubules & medulla) and has a paracrine function Maintains GFR by inducing vasodilation of afferent arterioles ```
37
What is the extrinsic regulation of GFR? (2)
Hormonal mechanism Activation of the RAAS occurs when systemic BP (and consequently GFR) is low Juxtaglomerular cells release renin Renin catalyses a cascade that increases systemic BP, renal perfusion and GFR Neural controls Sympathetic nervous system acts upon kidneys when systemic BP is low (baroreceptor reflex) Renal sympathetic nerves activate B1-adrenergic receptors on juxtaglomerular cells Renin release catalyses a cascade that increases systemic BP, renal perfusion and GFR
38
What is the exception of extrinsic regulation of GFR?
Occurs when ECF volume is extremely low i.e. circulatory shock Cerebral & cardiac perfusion prioritised over renal (shunting of blood) Prolonged reduction in perfusion can result in renal damage
39
What is reabsorption?
Selective reclaiming of filtrate components (return from tubule back to the blood)
40
Where does reabsorption occur?
Occurs through or between tubule cells
41
Is the process of reabsorption active or passive?
Depending on the substance reabsorbed, the process is active (requires ATP) or passive Active processes: primary & secondary active transport Passive processes: osmosis, diffusion, facilitated diffusion
42
What is the transport maximum (Tm)?
a limited amount of transport proteins are available for the reabsorption of a particular substance
43
Which cells are most specialised for reabsorption?
Tubule cells of the PCT are most specialised for reabsorption
44
What is the passive transport of reabsorption at the PCT?
Passive transport: Water (65% of filtrate volume) Ions: Cl-, K +, Ca2+ Urea (reabsorbed here, but later secreted back into filtrate)
45
What is the active transport of reabsorption at the PCT?
Active transport: Na +, HCO3- Glucose, amino acids, vitamins
46
What is the passive transport of reabsorption at the Loop of Henle?
Passive transport: Water Ions: Ca2+
47
What is the active transport of reabsorption at the Loop of Henle?
Active transport: | Ions: Na+, Cl-, K+
48
What is the mechanism of loop diuretics?
(e.g. frusemide) inhibit the transport protein for Na+/Cl-/K+ in the ascending limb This interferes with the medullary osmotic gradient (kidneys unable to produce concentrated urine)
49
Where does hormone-regulated reabsorption of water & electrolytes occur?
the DCT & CD
50
Where is antidiuretic hormone released and what is its function?
Released by the posterior pituitary in response to increased ECF osmolarity (dehydrated state) Increases the permeability of the DCT & CD to water, by inserting aquaporins (water channels) into the apical membrane of tubule cells ADH release is reduced in the overhydrated state Caffeine and alcohol inhibit the release of ADH
51
Where is aldosterone released and what is its function?
Released by the cortex of the adrenal gland as part of the RAAS (initial stimulus: low blood pressure) Aldosterone is also released in response to hyperkalaemia Aldosterone enhances the (active) reabsorption of Na+ at the DCT & CD Reabsorption of Na+ is coupled to K+ secretion
52
Where is atrial natiuretic peptide released and what is its function?
ANP is produced by cardiac atrial cells and released when blood volume/pressure is elevated Directly inhibits the reabsorption of Na+ at the DCT & CD
53
What is the function of parathyroid hormone?
Increases the (passive) reabsorption of Ca2+ at the DCT
54
What is secretion?
Movement of selected substances from the peritubular capillaries through the tubule cells into the filtrate Some substances (e.g. HCO3-) are synthesised by tubule cells and secreted directly
55
What are secreted substances? (4)
Certain drugs Undesirable metabolites reabsorbed by passive processes Urea, uric acid Excess K+ Driven by aldosterone at the DCT & CD Acids and bases (depending on blood pH) H +, NH4+ HCO3-
56
What are ureters?
Paired, narrow tubes with a thick muscular wall ~25 cm long Convey urine from the kidneys to the bladder ~1,200ml per day Upper half is in the abdomen, lower half in pelvis Abdominal part extends from the kidney to the bifurcation of the common iliac artery Urine is propelled by the peristaltic contractions of smooth m. as well as the filtration pressure of the glomeruli
57
What is the pathway of the ureters?
Retroperitoneal: covered anteriorly by parietal peritoneum They run inferiorly along the psoas m. and cross the front of the genitofemoral nerve (L1-2) The ureters leave the psoas m. near the bifurcation of the common iliac a. and pass over the SIJ to enter the pelvis Terminal parts pierce the posterior lateral angle of the bladder In males, the ureters are crossed by the vas deferens before they enter the bladder.
58
What is the arterial supply to the ureters?
Upper part: ureteric branch of the renal artery Middle part: branches from the abdominal aorta; gonadal, common iliac & internal iliac aa Lower part: branches from the superior and inferior vesical aa, uterine aa
59
What is the venous drainage of the ureters?
Veins that have the same names and serve the same areas as the arteries above
60
What is the lymphatic drainage of the ureters?
Abdominal portion: para-aortic lymph nodes, | Pelvic portion: common iliac & internal iliac lymph nodes
61
What is the nerve supply of the ureters?
Sympathetic: T10 – L2 via renal, coeliac and hypogastric plexuses Parasympathetic: Pelvic splanchnic nn, S2 - S4 Visceral afferents
62
What is the histology of the ureters? (3)
MUCOSA Transitional epithelium – continuous with the mucosae of the renal pelvis and bladder MUSCULARIS Internal longitudinal layer External circular layer An additional external longitudinal layer is present in the lower 1/3 SEROSA/ADVENTITIA Serosa seen in aspects of the ureter in contact with peritoneum
63
What is transitional epithelium and where is it found?
Found in the renal pelvis, ureters and bladder Cells of the basal layer are cuboidal or columnar Apical cells vary in appearance, depending on the degree of distension i.e. their appearance transitions between stratified cuboidal and stratified squamous epithelia In the relaxed state, this type of epithelium appears ~6 cell layers thick In the stretched state (distended with urine), it appears only 2 or 3 cells thick (although the actual number of cells remains constant)
64
What is the bladder?
A hollow organ with strong muscular walls Serves as a temporary reservoir for urine: Moderately full bladder holds 500mL Max. capacity 800-1000 mL
65
Where is the bladder located?
The size, shape and position of the bladder depends on the volume of its contents: When empty it is situated within the entire pelvic cavity As it distends it domes up into the abdominal cavity (a full bladder may even reach the level of the umbilicus) Lies in front of the rectum (M) or vagina (W)
66
What is the gross structure/regions of the bladder? (5)
APEX Points anteriorly to the top of the pubic symphysis Separated from the pubic bones by the potential retropubic space Median umbilical ligament (remnant of urachus) BASE/FUNDUS Formed by the posterior wall and is convex BODY Part between the apex and the fundus NECK Formed where the base and two inferolateral surfaces meet It is pierced by the urethra at the internal urethral orifice TRIGONE (L. ‘triangle’) A triangular region at the base of the bladder Area between the two ureteral orifices* and the internal urethral orifice The trigone lacks rugae (it has a smooth appearance) *Flaps of bladder mucosa act as valves and prevent vesicoureteric reflux
67
What are the 4 surfaces of the bladder?
1x inferoposterior (base), 2x inferolateral and 1x superior surface
68
What are the bladder relations? (2)
Peritoneum: The superior surface and 1 cm of the base of the bladder are the only parts covered with peritoneum The rest of the bladder is subperitoneal and sits above the pelvic floor Fascia: The entire organ is surrounded by fascia known as the vesical fascia (L. ‘little blister’) The vesical venous plexus, lies within this fascia on the side of the bladder
69
Discuss the male bladder
Prostate gland: located below the bladder Between the posterior surface and rectum: seminal vesicles, vas deferens, rectovesical pouch
70
Discuss the female bladder
In females the bladder is in contact with uterus and the vagina Uterovesical pouch: separates the bladder from the uterus in females (shallow, empty pouch).
71
What is the histology of the bladder? (3)
MUCOSA Bladder is lined with transitional epithelium that is thrown into numerous folds (rugae) in the relaxed state MUSCULARIS The smooth muscle of the bladder is referred to as detrusor muscle (L. ‘to thrust’) Three layers of smooth muscle Inner and outer layers of longitudinally arranged mm fibres Middle layer of circular arranged mm fibres These layers may be difficult to identify in the cadaver ADVENTITIA Variable amounts of perivesical fat
72
What is the arterial supply of the bladder?
Branches of the internal iliac aa: Superior vesical aa - supply the anterosuperior parts of the bladder Supply to fundus & neck: inferior vesical aa (M) or vaginal aa (F)
73
What is the venous drainage fo the bladder?
The names of the veins correspond to the names of the arteries They are tributaries of the internal iliac vein
74
What is the lymphatic drainage of the bladder?
Superior surface of the bladder drained by external iliac lymph nodes Fundus --> internal iliac lymph nodes
75
What is the nerve supply of the bladder?
Nerves from the vesical plexus, which is continuous with the hypogastric plexus Parasympathetics: pelvic splanchnic n (S2-S4) Motor supply to detruser mm and inhibitory to the internal urethral sphincter Sympathetics (T10 - L2) Visceral afferents
76
Describe the male urethra:
Serves both urinary & reproductive function ~20 cm long (much longer than the female urethra) Extends from the bladder neck to the urethral orifice at the tip of the penis Passes through the prostate and the entire corpus spongiosum Consists of 3/4 parts: Preprostatic & Prostatic Intermediate (membranous) Spongy (penile)
77
What is the prostatic urethra?
~2-4 cm in length The urethra runs closer to the anterior surface of the prostate Receives the openings of the ejaculatory ducts (the union of the vas deferens and ducts of the seminal vesicles bilaterally)
78
What is the Intermediate (membranous) urethra?
~1-2 cm in length Runs from the apex of the prostate to the bulb the penis, where it is continuous with the spongy urethra Bulb of penis: expanded proximal portion of the corpus spongiosum Surrounded by the external urethral sphincter and the perineal membrane Located posterolaterally: the paired bulbourethral glands and their ducts (these open into the beginning of the spongy urethra)
79
What is the spongy (penile) urethra?
Longest region ~15 cm Passes though the bulb and corpus spongiosum of the penis Bulbourethral ducts open into its dilated, proximal region Many mucous-secreting glands are located along its length Ends at external urethral orifice (narrowest part of the urethra) Just proximal to the EUO is a short dilated region called the navicular fossa
80
What is the internal urethral sphincter?
Formed by thickening of the detrusor smooth m. at the neck of the bladder Involuntary sphincter (autonomic control) SNS keeps the IUS tonically contracted Prevents leaking between voiding, retrograde ejaculation PNS causes the IUS to relax
81
What is the external urethral sphincter?
Composed of striated muscle and is under voluntary control Innervated by the perineal branch of the pudendal nerve (S2-S4) Maintains constant muscular tone and only relaxes during micturition It surrounds the membranous urethra where it passes through the striated muscle of the pelvic floor The levator ani mm (voluntary m.) also contributes to urinary continence
82
What is the histology of the urethra?
MUCOSA Most of the male urethra is lined by transitional epithelium (typical of the urinary tract) An exception is the navicular fossa where the epithelium is stratified squamous epithelium This is continuous with the stratified squamous epithelium of the glans penis Mucous-secreting glands produce a protective mucous layer. MUSCULARIS The urethral smooth muscle is a continuation of the involuntary smooth muscle of the bladder
83
What is the arterial supply to the urethra?
Internal pudendal a. (from internal iliac a)
84
What is the venous drainage of the urethra?
Internal pudendal veins
85
What is the lymphatic drainage of the urethra?
Internal iliac, deep inguinal and external iliac nodes
86
What is the nerve supply go the urethra?
Spongy urethra & EUS: pudendal n. (S2-S4) Intermediate & prostatic urethra: autonomic fibres from the inferior hypogastric plexus Sympathetic: T10-L2 Parasympathetic: Pelvic splanchnic n (S2-4) Visceral afferents
87
Describe the female urethra:
Serves a urinary function only Is relatively short ~4cm (greater incidence of urinary tract infections in females) A straight muscular tube which passes in an anteroinferior direction from the bladder neck to the external urethral orifice (EUO is anterior to the vaginal orifice and posterior to the clitoris) Most of the urethra is embedded within the anterior vaginal wall The walls of the urethra are in contact except during urination
88
What are the 2 urethral sphincters?
Internal urethral sphincter | External urethral sphincter
89
Describe the internal urethral sphincter
Located at the bladder-urethra junction, formed by the continuation of detrusor m. Under involuntary control (autonomic nervous system)
90
Describe the external urethral sphincter
Formed by circular, striated muscle Surrounds the urethra where it passes through the pelvic floor It is supplied by the pudendal nerve (S2-S4) and is under voluntary control Levator ani mm also contribute to urinary continence
91
Describe the histology of the urethral sphincters (2)
MUCOSA Lined by non-keratinized stratified squamous epithelium Mucous glands are also situated in the wall of the urethra The largest of these are the paired paraurethral glands PARAURETHRAL GLANDS Are histologically homologous to the prostate gland These glands are drained by a common duct (one on each side) just inside the external meatus or orifice
92
What is the arterial supply of the urethral sphincters?
Upper part: Vaginal arteries | Lower part: Internal pudendal arteries
93
What is the venous drainage of the urethral sphincters?
Into the vesical plexus  internal pudendal veins
94
What is the lymphatic drainage of the urethral sphincters?
Drain mainly into the internal iliac lymph nodes | Some into the external iliac lymph nodes
95
What is the nerve supply of the urethral sphincters?
IUS: autonomic nerves from inferior hypogastric plexus Sympathetic & Parasympathetic EUS: pudendal nerve S2-S4
96
What is micturition?
Also referred to as urination or voiding In infants, urination is mediated by a simple spinal reflex (involuntary control) By age 2-3, descending circuits from higher brain centres mature enough to override reflexive urination (involves the SNS, PNS & somatic nervous system) The micturition and storage centres are located in the pons
97
What are the 3 events of micturition?
Contraction of the detrusor muscle Relaxation of the IUS Relaxation of the EUS

Yr 3 Sem 1 (7 decks)

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