Urine Formation Flashcards
(116 cards)
1
Q
What is the primary function of the kidneys?
A
To rid the body of waste materials and control the volume and composition of body fluids
This includes filtering plasma and excreting unwanted substances in urine while returning needed substances to the blood.
2
Q
What substances do the kidneys excrete?
A
- Urea
- Creatinine
- Uric acid
- End products of hemoglobin breakdown
- Metabolites of various hormones
These substances are considered metabolic waste products and foreign chemicals.
3
Q
What is the functional unit of the kidney?
A
Nephron
4
Q
What are the two principal types of nephrons in the mammalian kidney?
A
- Cortical nephrons
- Juxtamedullary nephrons
These types are classified based on the location of their glomeruli and the depth of their loops of Henle.
5
Q
What is the role of the glomerular capsule?
A
It collects the glomerular filtrate from the glomerulus
6
Q
What is the function of the vasa recta?
A
To play an essential role in the formation of concentrated urine
7
Q
How much of the cardiac output is normally supplied to the kidneys?
A
22%
8
Q
What is the glomerular filtration rate (GFR) in humans?
A
About 125 ml/min
9
Q
What is the filtration fraction?
A
The percentage of the renal plasma flow that becomes glomerular filtrate
Normal plasma flow through both kidneys is 650 ml/min, with a GFR of 125 ml/min, hence the average filtration fraction is 19%.
10
Q
What three factors determine the filtration pressure in the kidneys?
A
- Glomerular pressure
- Plasma colloidal osmotic pressure (COP)
- Bowman’s capsular pressure
11
Q
True or False: Afferent arteriolar constriction increases GFR.
A
False
12
Q
What effect does sympathetic stimulation have on GFR?
A
Decreases GFR
13
Q
What is meant by autoregulation of RBF and GFR?
A
The ability of renal blood flow and glomerular filtration rate to remain relatively constant despite changes in systemic arterial pressure
This intrinsic mechanism is independent of nerve supply.
14
Q
According to the myogenic theory, what happens to arterioles when blood pressure increases?
A
Arterioles contract
15
Q
What is the role of renin in the kidneys?
A
To regulate blood pressure and GFR through the renin-angiotensin system
16
Q
What are the three processes involved in the formation of urine in the nephrons?
A
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
17
Q
What layers compose the glomerular capillary membrane?
A
- Endothelium of the capillary
- Basement membrane
- Podocytes (epithelial cells)
This structure is relatively impermeable to proteins.
18
Q
What is the fluid filtered through the glomerular membrane into Bowman’s capsule called?
A
Glomerular fluid (GF)
Glomerular fluid is essentially protein-free and devoid of cellular elements.
19
Q
What are the three layers of the glomerular capillary membrane?
A
- Endothelium of the capillary
- Basement membrane
- Podocytes
Podocytes are epithelial cells that form slit pores for glomerular filtrate passage.
20
Q
What are fenestrae?
A
Small holes in endothelial cells of the glomerulus
Fenestrae increase permeability to water and small solutes.
21
Q
What is the permeability of the glomerular membrane compared to usual capillaries?
A
100 to 1000 times greater
This is due to the size of pores in the endothelium and slit pores.
22
Q
What is the maximum diameter of molecules that can pass through the glomerular membrane?
A
8 nm
Larger molecules, such as plasma proteins, are completely impermeable.
23
Q
What is the primary force driving glomerular filtration?
A
Hydrostatic pressure of blood
Colloidal osmotic pressure also plays a role in opposing filtration.
24
Q
What is the average colloidal osmotic pressure in the glomerular capillaries?
A
32 mm Hg
This pressure increases as blood passes from the arterial to venous end.
25
How is filtration pressure calculated?
Filtration pressure = Glomerular pressure - (Colloidal osmotic pressure + Capsular pressure)
## Footnote
Example: If Glomerular Hydrostatic Pressure = 60 mm Hg, Colloidal Osmotic Pressure = 32 mm Hg, and Capsular Pressure = 18 mm Hg, then Filtration pressure = 60 - (32 + 18) = 10 mm Hg.
26
What is tubular reabsorption?
Transport of water and solutes from tubular fluid to peritubular capillaries
## Footnote
More than 90% of water in GF is reabsorbed.
27
What are the two basic mechanisms of tubular absorption?
* Active transport
* Passive transport
## Footnote
Active transport requires energy, while passive transport relies on concentration gradients.
28
What is the role of the Na+-K+ ATPase in sodium reabsorption?
It actively transports Na+ from tubular epithelial cells to the peritubular space
## Footnote
This creates a chemical gradient for Na+ movement.
29
What is the typical reabsorption percentage of sodium in the proximal tubule?
65%
## Footnote
This is essential for maintaining electrolyte balance.
30
What is the mechanism of glucose and amino acid reabsorption?
Symport or co-transport
## Footnote
This involves Na+ binding and requires specific carriers.
31
What is the renal threshold for glucose?
175 mg/dl
## Footnote
Exceeding this threshold leads to glucose appearing in urine.
32
What is the function of the urinary bladder?
Provides an expandable reservoir for urine
## Footnote
It accommodates urine without significant increases in internal pressure.
33
What is micturition?
The process of emptying the urinary bladder
## Footnote
It occurs when bladder pressure reaches a certain threshold.
34
What initiates peristaltic contraction in the ureters?
Increased pressure in the pelvis of the kidney
## Footnote
This contraction propels urine towards the bladder.
35
What prevents the reflux of urine from the bladder?
Ureterovesicular valve
## Footnote
This valve is located at the junction of ureter and bladder.
36
What happens when the bladder pressure reaches 150 mm water?
Contraction of bladder wall begins and sphincter relaxation occurs
## Footnote
This leads to urination.
37
What role do sympathetic and parasympathetic nerves play in bladder function?
Sympathetic decreases frequency of peristalsis; parasympathetic increases it
## Footnote
Both divisions of ANS innervate the bladder.
38
What is the maximum transport rate for glucose reabsorption known as?
Transport maximum (Tm)
## Footnote
For glucose, Tm is 320 mg/min.
39
What percentage of urea is reabsorbed in the proximal tubule?
50%
## Footnote
Urea reabsorption is less than that of water and sodium.
40
What is the unique characteristic of K+ transport in the nephron?
It is reabsorbed in some parts and secreted in others
## Footnote
K+ is reabsorbed in the proximal tubule and secreted in the distal nephron.
41
What supplies the bladder from the autonomic nervous system?
Nerves from sympathetic and parasympathetic divisions of ANS
## Footnote
Preganglionic sympathetic fibers leave from spinal cord in 2nd to 4th lumbar nerves to the posterior mesenteric ganglion
42
What is the role of parasympathetic nerves in bladder function?
Cause contraction of whole bladder and are main motor nerves
## Footnote
They are inhibitory to the internal sphincter
43
What two reflex systems are involved in complete emptying of the bladder?
Maintenance of bladder muscle contraction and sphincter relaxation
## Footnote
Achieved through reflexes from receptors in bladder walls and urethra
44
What does uremia or azotemia indicate?
Elevated level of waste products in the blood, particularly nitrogen-containing compounds
## Footnote
Includes substances like urea and creatinine
45
What are some causes of uremia or azotemia?
* Renal failure
* Increased production of urea
* Decreased elimination of urea
* Dehydration
* Chronic infection of the kidney
46
Which condition is characterized by difficult or painful micturition?
Dysuria
## Footnote
Other conditions include diuresis, polyuria, oliguria, anuria, and stranguria
47
What is renal clearance?
Measurement of the kidney’s ability to remove substances from the plasma
## Footnote
Used to determine various renal function metrics like GFR and RPF
48
What is plasma clearance?
Expresses the ability of the kidneys to clean or clear the plasma of various substances
## Footnote
Example: If 1 mg of a substance is excreted into urine each minute, then 1 ml/min of plasma is cleared
49
What substance is commonly used to estimate GFR?
Inulin
## Footnote
It must be freely filtered at the glomerulus and not reabsorbed or secreted by tubular epithelium
50
What is the purpose of measuring renal plasma flow (RPF)?
To assess the kidney's ability to handle substances that are filtered and secreted
## Footnote
Para Amino Hippuric acid (PAH) is commonly used for this measurement
51
What is the counter current mechanism in the kidney?
A system where inflow of fluid runs parallel to, counter to, and in close proximity to outflow
## Footnote
Involves the Loops of Henle and vasa recta
52
What is the primary mechanism for concentrating urine?
Reabsorption of water facilitated by ADH and high osmolarity of renal medullary fluid
## Footnote
This creates an osmotic gradient for water reabsorption
53
What regulates water conservation in the kidneys?
ADH (Antidiuretic Hormone)
## Footnote
Synthesized in the hypothalamus and released in response to increased plasma osmolality
54
What is the effect of aldosterone on renal function?
Increases Na+ reabsorption and K+ excretion in tubules
## Footnote
It acts on distal tubules and is influenced by dietary sodium intake
55
What triggers the renin-angiotensin system?
Reduced circulating blood volume or decreased sodium concentration
## Footnote
This system is crucial for regulating blood pressure and fluid balance
56
What happens during the excretion of dilute urine?
Reabsorption of solutes occurs without significant water reabsorption
## Footnote
Urine concentration can be as low as 50 mOsm/L
57
What characterizes the formation of concentrated urine?
High levels of ADH and high osmolarity of renal medullary fluid
## Footnote
This allows for significant water reabsorption in the presence of ADH
58
What is the role of the vasa recta in urine concentration?
Acts as a countercurrent exchanger, retaining solutes in the medulla
## Footnote
Blood flow is sluggish to maintain the osmotic gradient
59
What hormone is released in response to pain?
ADH
## Footnote
ADH stands for Antidiuretic Hormone, which helps regulate water balance in the body.
60
What is the primary function of aldosterone?
Regulates K+ and Na+ concentration
## Footnote
Aldosterone acts on tubules to cause Na+ reabsorption and K+ excretion.
61
What triggers the activation of renin in the renin-angiotensin system?
Reduced circulating blood volume, decreased sodium concentration, sympathetic stimulation
## Footnote
These factors stimulate the release of renin, which is crucial for blood pressure regulation.
62
What effect does parathyroid hormone have on phosphate reabsorption?
Decreases phosphate reabsorption
## Footnote
Parathyroid hormone increases phosphate excretion in urine.
63
What is the role of atrial natriuretic peptide (ANP)?
Increases GFR, inhibits Na+ and water absorption, reduces water reabsorption, inhibits aldosterone release
## Footnote
ANP is released when the atria are stretched due to high blood volume.
64
Which hormone regulates erythropoiesis?
Erythropoietin
## Footnote
Erythropoietin is produced in the kidneys.
65
What is the normal blood pH?
7.4
## Footnote
Maintenance of normal blood pH is essential for homeostasis.
66
Name the three primary buffer systems involved in acid-base balance.
Chemical buffer systems, respiratory regulation, renal control
## Footnote
Each system plays a critical role in maintaining pH balance in the body.
67
What is the most important buffer system in the body?
Bicarbonate buffer system
## Footnote
Bicarbonate combines with H+ ions to help maintain pH.
68
What is the role of the phosphate buffer system?
Buffers renal tubular fluid and intracellular fluid
## Footnote
It consists of HPO42- (base) and H2PO4– (weak acid).
69
How do proteins act as a buffer in the blood?
Hemoglobin binds with H+ ions to form HHb
## Footnote
This reaction helps to stabilize blood pH.
70
What is the ammonia buffer system's role in the kidneys?
Forms NH4+ ions from glutamine
## Footnote
NH4+ ions are excreted as ammonium chloride in the urine.
71
How does the respiratory system regulate acid-base balance?
Adjusts PCO2 levels
## Footnote
Changes in ventilation affect H+ ion concentration and pH.
72
What happens during metabolic acidosis?
Gain of strong acid or loss of base
## Footnote
Conditions like diabetes and renal acidosis can lead to metabolic acidosis.
73
What is metabolic alkalosis characterized by?
Gain of base or loss of strong acid
## Footnote
Persistent vomiting and K+ deficiency can cause metabolic alkalosis.
74
What occurs during respiratory acidosis?
Inability of lungs to excrete CO2
## Footnote
This condition is often caused by respiratory depression or obstruction.
75
What is the result of respiratory alkalosis?
Low plasma PCO2 and alkalemia
## Footnote
Caused by hyperventilation or abnormal stimuli to respiratory centers.
76
What percentage of water by weight does an adult contain?
60%
## Footnote
This percentage can vary based on age and body fat.
77
What are the three compartments of body fluid?
Intracellular fluid, interstitial fluid, plasma
## Footnote
These compartments help maintain fluid balance in the body.
78
What effect does adding isotonic NaCl solution have on body fluids?
Equal distribution of water between compartments
## Footnote
This is due to osmotic pressure balance.
79
What percentage of water is present intracellularly?
Approximately 60%
## Footnote
This is the general distribution of water in the body.
80
What are transcellular fluids?
Fluids such as CSF, aqueous humor, synovial fluids, urine, bile
## Footnote
These fluids are distinct from intracellular and extracellular fluids.
81
What happens when an isotonic NaCl solution is added to the ECF?
Equal distribution of water extracellularly and intracellularly occurs.
82
What is the effect of adding a hypertonic NaCl solution?
Water shifts into the plasma.
83
What is the primary method by which the body gains water?
Ingestion or as an end product of cellular metabolism.
84
What are the major electrolytes found in the body?
* Sodium
* Potassium
* Calcium
* Magnesium
* Chloride
* Phosphate
* Sulphate
* Bicarbonate
85
What is the major cation of extracellular fluid (ECF)?
Sodium.
86
What mechanisms maintain sodium equilibrium in the ECF?
* Short-term control via ADH-thirst control system
* Long-term control via ingestion and urinary excretion
87
What triggers the release of ADH in relation to sodium levels?
If ECF sodium rises.
88
What is 'salt hunger'?
A strong behavioral drive to salt seen in sodium-deficient animals.
89
What stimulates the release of aldosterone?
A decrease in plasma sodium and blood pressure.
90
What is the main function of aldosterone in sodium regulation?
Enhances reabsorption of sodium from the renal tubule.
91
How is sodium primarily excreted?
Filtered at the glomerulus and mostly reabsorbed in the renal tubules.
92
What effect does an increase in arterial blood pressure have on sodium excretion?
Inhibits renin and aldosterone release, increasing sodium excretion.
93
What is the major cation of intracellular fluid (ICF)?
Potassium.
94
What regulates potassium concentration?
Aldosterone.
95
What happens to potassium secretion when there is increased hydrogen ion secretion?
Depresses potassium secretion.
96
What is the role of chloride and bicarbonate in electrolyte balance?
They are balanced electrically with sodium ions.
97
What are the two major types of nephrons in birds?
* Reptilian type
* Mammalian type
98
What is unique about the renal portal system (RPS) in birds?
Provides an extra branch of blood flow to renal tubules.
99
What is the metabolic end product of protein and amino acids in birds?
Uric acid.
100
What is the primary function of lymph?
* Reabsorption of fluid
* Filtering harmful agents
* Transporting fatty substances
101
What percentage of fluid from the capillary bed is reabsorbed?
About 90%.
102
What is cerebrospinal fluid (CSF) formed by?
The choroid plexus of the ventricles of the brain.
103
What is the primary function of CSF?
* Nutritive medium for the brain
* Cushioning against shock
104
What are the three types of joints?
* Fibrous Joints
* Cartilaginous Joints
* Synovial Joints
105
What do synovial joints have that allows for movement?
A capsule with an outer fibrous layer and synovial membrane.
106
What are synovial joints?
Freely movable joints, e.g., shoulders joint, stifle joint
## Footnote
Synovial joints allow for a wide range of motion and are characterized by a joint capsule.
107
What is the role of muscles, ligaments, and tendons in synovial joints?
They control and unite the movement of the joint
## Footnote
These structures provide stability and facilitate movement.
108
What is the structure of the capsule in synovial joints?
An outer fibrous layer consisting of collagen fibres
## Footnote
The fibrous layer connects the periosteum of one bone to another.
109
What is the function of ligaments in synovial joints?
To stabilize the joint and limit its range of motion
## Footnote
Ligaments are located in and around the joint capsule.
110
What is the synovial membrane?
The inner lining layer of the joint surface
## Footnote
It produces synovial fluid that lubricates the joint surfaces.
111
What is synovial fluid?
A transparent viscous liquid that lubricates joint surfaces
## Footnote
It is produced by the synovial membrane.
112
What are menisci?
Special areas of dense fibrocartilage between articulating cartilage surfaces
## Footnote
They cushion compressive forces acting on the ends of the bones.
113
What is the composition of synovial fluid?
Contains albumin, globulin, mucin, and hyaluronic acid but no fibrinogen
## Footnote
These components assist in lubrication and nourishment of cartilage.
114
What is the primary function of synovial fluid?
To reduce friction in the joints and nourish the articular cartilages
## Footnote
This function is critical for joint health and mobility.
115
True or False: Synovial fluid is found only in joint cavities.
False
## Footnote
Synovial fluid is also found in tendon sheaths and bursae.
116
Fill in the blank: The outer fibrous layer of the synovial capsule consists of _______.
collagen fibres
## Footnote
These fibres provide strength and stability to the joint.
