Exam 3: Urinary & Digestive Flashcards
Functions of the Kidneys
Filters blood, excreting toxic metabolic wastes
Regulates blood volume, pressure, and osmolarity
Regulates electrolytes
Regulates pH balance
Secretes erythropoietin
Regulates Ca2+ levels
Clears hormones from the blood via urination
Detoxifies free radicals
Peristaltic Contraction
A wave contraction from one end of the ureter to the other, ensuring constant outflow. This same contraction occurs in the intestines.
What Nitrogenous Wastes are removed through urination?
Urea, Uric Acid, & Ammonia
Urea Formation Steps
Proteins -> Amino Acids -> NH2 removed -> Ammonia
Ammonia is converted to Urea by the liver
Urea can be converted to Uric Acid
Major Nitrogenous Wastes
Ammonia - Most toxic when abundant in the body
Urea - Formed from converted Ammonia, less toxic
Uric Acid - Product of Nucleic Acid Catabolism
Creatinine - Product of creatine phosphate catabolism
Where does filtration occur in the kidneys?
Filtration starts in the cortex and then moves into the medulla via nephrons. Most of the work occurs in the medulla.
What are calyxes
Dumping stations where anything that enters becomes urine. There is no more filtration, secretion, or absorption from the calyx to the urethra.
Why is the kidney highly vascularized?
There is constant filtration occurring, which is highly metabolic and requires more blood flow. They receive about 21% of all cardiac output
What is the route of Renal Circulation?
Renal Artery, Segmental Artery, Interlobar Artery, Arcuate Artery, Cortical Radiate Artery, Afferent Artery, Glomerulus, Efferent Arteriole, Peritubular Capillaries or Vasa Recta, Cortical Radiate Vein, Arcuate Vein, Interlobar Vein, Renal Vein
Where does O2 transport occur in the Kidneys?
Peritubular Capillaries, after blood passes through them it is deoxygenated and begins venous return
How is the Glomerulus Capillary Bed different from others?
The Glomerulus is for filtration, only moving sugars and not O2/CO2
What are the two principal parts of a nephron and what are their functions?
Renal Corpuscle (Glomerulus) - Filters the blood plasma
Renal Tubule (PCT, Loop, DCT) - A long, coiled tube that converts the filtrate into urine
Glomerular Capsule Layers and Tissue Types?
Parietal Layer - Simple Squamous Epithelium
Visceral Layer - Podocyte cells provide structure and support to keep the capillaries from tearing under high-pressure
Types of Nephrons and their Abundance
Juxtamedullary Nephrons - 15% of all nephrons
Cortical Nephrons - 85% of all nephrons
Juxtamedullary Nephrons
Better at conserving water
Efferent Arterioles branch into the vasa recta
The loop branches down farther into the medulla
Longer of the two types
Cortical Nephrons
Shorter of the two types
Efferent arterioles branch into peritubular capillaries
Stages of Urine Formation
1) Glomerular Filtration: Ultra-filtration Filtration is driven by BP where small molecules (Ca2+, Na+, K+, glucose, Mg+, H2O) are pushed out to the proximal tubule and large proteins and cells remain in the blood.
2) Tubular Reabsorption: Useful molecules are transported from the tubule to the blood
3) Tubular Secretion: Waste from the blood is moved to the tubule
4) Water Conservation: Water is removed from the urine and returned to the blood
Hydration and Water Conservation
Dehydration causes an increase in water conservation
Overhydration causes a decrease in water conservation
Glomerular Filtration Membranes
Fenestrated Endothelium: Highly permeable with large filtration pores, doesn’t let blood cells through
Basement Membrane: Proteoglycan gel with a negative charge that repels albumin and has very small filtration pores
Filtration slits: Openings through podocytes that are medium in size and negatively charged. Increases the rate of flow out of the capillaries
Molecule Size and Glomerular Filtration
Any molecule smaller than 3 nm can pass freely through the membrane. This includes water, electrolytes, glucose, fatty acids, amino acids, nitrogenous wastes, and vitamins
Some substances of low molecular weight are bound to the plasma proteins and cannot get through the membrane. This includes calcium, iron, and thyroid hormone. If these molecules are unbound, they pass through.
Forces involved in Glomerular Filtration
Blood Hydrostatic Pressure (BP) is the only force driving substances out of the capillary
Colloid Osmotic Pressure is a concentration pressure from the surrounding fluids (H2O) pushing back into the capillary
Capsular Pressure is the hydrostatic pressure that pushes back into the capillary.
If BP falls too low, the kidneys will not work due to the lack of pressure driving fluid through the glomerulus.
Adding all three forces gives us Net Filtration Pressure, which must be positive
Glomerular Filtration Rate
The amount of filtrate formed per minute by both kidneys. The total amount of filtrate produced per day is about 50-60 times the amount of blood in the body, though nearly all of it is reabsorbed.
Why is it important to regulate the Glomerular Filtration Rate?
If GFR is too high, fluid cannot reabsorb. Urine output will also rise, potentially leading to dehydration and electrolyte depletion.
If GFR is too low, wastes are reabsorbed rather than expelled to the bladder
Methods of GFR Control
Renal Autoregulation
Sympathetic Control
Hormonal Control
Renal Autoregulation
The ability of the nephrons to adjust their blood flow and GFR through the myogenic mechanism and tubuloglomerular feedback
The myogenic mechanism is the ability of the smooth muscle to contract when stretched. When BP rises, arterioles stretch and then constrict. When BP falls, arterioles relax and dilate.
Tubuloglomerular feedback is received based on the concentration of molecules in the tubular fluid. It is the communication between macula densa cells and granular cells
Tubuloglomerular Feedback
Macula Densa cells detect NaCl concentrations in the filtrate. When GFR is high, NaCl cannot be reabsorbed, thus concentration is high. This leads to macula densa cells absorbing the NaCl and in turn, they secrete ATP.
This ATP is metabolized and turned into Adenosine which stimulates granular cells.
Granular (Juxtaglomerular) cells wrap around the afferent arteriole and respond to Adenosine. When Adenosine is detected, the cells constrict the afferent arteriole, reducing blood flow and correcting GFR
Sympathetic Controlof GFR
Sympathetic Nerve Fibers innervate the renal blood vessels and constrict the afferent arterioles during strenuous exercise or in conditions like circulatory shock. This constriction reduces GFR and urine output and redirects blood to the heart, brain, and skeletal muscles.
Renin-Angiotensin-Aldosterone Mechanism
The Kidneys release renin from granular cells when pressure or GFR drop
Angiotensin from the liver interacts with the Renin to produce Angiotensin I, which is then converted to Angiotensin II via Angiotensin-Converting Enzyme (ACE) found in the lungs and kidneys
Angiotensin II acts on the body to raise BP
Angiotensin II Effects on BP
Acts on the hypothalamus to induce thirst. Higher H2O intake will raise BP
Acts on the cardiovascular system, causing vasoconstriction and raising BP
Acts on the Adrenal Cortex of the Kidneys, stimulating the release of Aldosterone, promoting Na+ and H2O retention, and increasing BP
Acts on the posterior pituitary to secrete ADH, which promotes water reabsorption by the collecting duct
Proximal Convoluted Tubule
The PCT reabsorbs (sends out of the tubule) roughly 65% of the glomerular filtrate, removes substances from the blood, and secretes them into the tubular fluid.
The PCT saves glucose, H2O, and sugar
Sodium is reabsorbed into the bloodstream, meaning H2O is as well
Peritubular Capillaries
Solutes and water that leave the basal surface of the tubular epithelium are reabsorbed by these capillaries via osmosis and solvent drag
Angiotensin II Effects on Tubular Reabsorption
Efferent arterioles are constricted, maintaining or increasing GFR and Glomerular BP
This constriction reduces BP in the peritubular capillary and reduces resistance to tubular reabsorption
Increased tubular reabsorption removes H2O from the tubules, decreasing urine volume but increasing concentration
Transport Maximum
When all of the transport proteins in the tubule cells are occupied, any remaining solutes will pass by and appear in the urine
In cases of hyperglycemia, all sugar transporters are saturated, resulting in a high sugar concentration in the urine
Tubular Secretion
The renal tubule extracts chemicals from peritubular capillary blood and secretes them into the tubular fluid
The purposes of secretion are acid-base balance, waste removal, and the clearance of drugs and contaminants
The Nephron Loop Functions
The primary function of the loop is to generate a salinity gradient that enables the collecting duct to concentrate the urine and conserve water. Water is saved by manipulating Na+.
The loop also plays a role in electrolyte reabsorption. The thick segment reabsorbs 25% of Na+, K+, and Cl- from the filtrate via active transport.
At the end of the loop, tubular fluid is very dilute because solutes were reabsorbed without water due to the impermeability of the thick segment.
Distal Convoluted Tubule & Collecting Duct functions
The DCT and Collecting Duct reabsorb water and salt through hormonal pathways.
Aldosterone in the DCT
Aldosterone is secreted by the Adrenal Cortex when Na+ concentration falls or K+ concentration rises.
When released, it acts on the thick segment of the nephron loop, the DCT, and the cortical portion of the collecting duct, stimulating reabsorption of Na+ and secretion of K+.
Water follows the Na+, reducing urine volume and increasing K+ concentration in the urine.
Atrial Natriuretic Peptides in the DCT
Made by the atrial myocardium in response to high blood pressure, Natriuretic Peptides help to dilate the afferent arteriole and constrict the efferent arteriole, increasing GFR.
It also inhibits the secretion of renin, aldosterone, and ADH along with inhibiting NaCl reabsorption by the collecting duct
ADH in the DCT
ADH is secreted by the posterior pituitary in response to dehydration, loss of blood volume, and increased blood osmolarity.
ADH makes the collecting duct more permeable to H2O, leading to increased water reabsorption, and decreasing urine output.
Alcohol’s effects on ADH
Alcohol inhibits ADH, resulting in an increase in urine output and leading to dehydration.
Parathyroid Hormone in the DCT
PTH is secreted from the parathyroid gland in response to Ca2+ deficiency in the blood.
PTH acts on the thick segment of the loop and the DCT to increase Ca2+ reabsorption.
PTH also acts on the PCT to increase phosphate secretion, resulting in more phosphate content in the urine.
H2O Reabsorption by the Collecting Duct
As tubular fluid flows through the collecting duct, it passes through increasingly concentrated medullary tissue fluid. This increasing osmolarity causes more H2O to flow out the farther down the fluid flows.
The CD is ALWAYS impermeable to H2O unless Aquaporins are opened by ADH
Water Diuresis effects on Urine
Drinking large volumes of water will produce a lot of hypotonic urine (high H2O, less Na+)
The Cortical portion of the CD reabsorbs NaCl, but it is impermeable to water, thus the H2O stays in the CD
Dehydration effects on Urine
Dehydration leads to hypertonic urine that is dark in color due to its high concentration.
High blood osmolarity from dehydration also stimulates the posterior pituitary to release ADH, which opens Aquaporins on the CD, resulting in more H2O reabsorption and a higher concentration of Na+ in the urine
Countercurrent Multiplier of the Nephron Loop
H2O flows out of the descending limb through passive diffusion (osmosis)
Na+ is removed from the ascending limb through active transport (NEEDS ATP)
The Na+ that is removed from the ascending limb increases the concentration of the surrounding tissues/fluids, resulting in more H2O flowing out of the descending limb.
Removed H2O and Na+ are reclaimed by the body
Muscles of the Urinary Bladder
Internal Sphincter: Smooth Muscle that is autonomously controlled by the brain
External Sphincter: Skeletal Muscle that can be controlled manually
The Process of Voiding Urine (Micturition)
As the bladder fills, the detrusor muscle in the bladder wall relaxes while the internal sphincter contracts. Both are caused by sympathetic activity in the lumbar spinal cord.
Somatic nerve fibers give the external sphincter voluntary control
The Micturition reflex is an involuntary spinal reflex that partly controls urination
Renal Insufficiency
A state in which the kidneys cannot maintain homeostasis due to the destruction of their nephrons.
Nephron destruction occurs due to hypertension, chronic kidney infections, trauma, prolonged ischemia and hypoxia, poisoning, blockage of renal tubules, atherosclerosis, or glomerulonephritis
Hemodialysis
The process of artificially clearing wastes from the blood through transplantation, though the risk of rejection is high.
Types of Homeostatic Balance (3)
Fluid Balance: Urination & Defecation results in H2O loss
Electrolyte Balance: Sweating causes loss of electrolytes
Acid-Base Balance: Respiration causes changes in blood pH
Fluid Compartments
65% of body fluid is in the intracellular fluid (inside cells)
35% of body fluid is in the extracellular fluid
- 25% in the interstitial fluid (between the outside of cells)
- 8% in the blood plasma and lymphatic fluid
- 2% in the transcellular fluid (CSF, synovial, pleural, pericardial, humors of the eye, etc.)
Osmotic Fluid Balance in the Body
Osmotic Balance is present between the intercellular and extracellular areas of the body. There is, however, ionic imbalance which is the driving force behind ion transport in the body.
Water Intake and Output
H2O intake is typically the same as water loss each day.
Effects of Dehydration
Dehydration increases blood concentration while reducing blood pressure
Highly concentrated blood stimulates hypothalamic osmoreceptors, reducing salivation and causing a sense of thirst.
Reduced BP stimulates Renin production, which leads to Angiotensin II formation, which stimulates the hypothalamic osmoreceptors, reducing salivation and causing thirst.
Effects of ADH on the blood
When blood osmolarity (Na+ concentration) increases, osmoreceptors in the hypothalamus stimulate the posterior pituitary to release ADH
Similarly, a decrease in plasma volume inhibits baroreceptors in the atrium and blood vessels which also stimulates the post. pituitary to release ADH
ADH targets the collecting ducts of the kidneys, increasing H2O absorption and resulting in an increase in osmolarity and plasma volume as well as scant urine
Effects of Aldosterone on the blood
When K+ concentration rises or Na+ concentration decreases, the Adrenal cortex is stimulated, releasing Aldosterone which targets the distal tubules of the kidneys
The distal convoluted tubules are affected, increasing Na+ reabsorption and K+ secretion
These effects restore homeostatic plasma levels of Na+ and K+
Effects of Atrial Natriuretic Peptide (ANP) on the blood
ANP is an “OPPOSITE MOLECULE” because it gets rid of H2O rather than reabsorbing it
High BP causes a stretch in the atria, which stimulates ANP release
ANP targets the JG Apparatus of the Kidney, reducing Renin release and resulting in less Angiotensin II, causing vasodilation and lowering BP
ANP targets the hypothalamus and posterior pituitary, decreasing ADH release, inhibiting the collecting duct, and decreasing Na+ and H2O reabsorption. This decrease in reabsorption also reduces blood volume, which lowers BP
ANP targets the Adrenal Cortex, which causes a decrease in the release of Aldosterone, inhibiting the collecting ducts and decreasing Na+ and H2O reabsorption which also reduces blood volume and BP
Renin-Angiotensin System and BP
Decreased stretch in the afferent arterioles and decreased NaCl concentration cause the granular cells of the kidney to release Renin.
Renin and Angiotensinogen (from the liver) interact to form Angiotensin II
Angiotensin II causes vasoconstriction in the systemic arterioles, increasing peripheral resistance
Angiotensin II also stimulates the Adrenal Cortex to secrete Aldosterone. This Aldosterone targets the DCT, causing increased Na+ & H2O reabsorption
Increased peripheral resistance raises BP. Increased Na+ and H2O reabsorption increases blood volume, which in turn raises BP
Neural Regulation (SNS) of BP
Decreased systemic BP inhibits the baroreceptors in blood vessels
This causes the sympathetic nervous system to stimulate the granular cells, starting the Renin-Angiotensin System
The SNS also stimulates the systemic arterioles, causing vasoconstriction and increasing peripheral resistance, raising BP
ADH release and its effects on BP
Systemic BP along with Angiotensin II stimulates the posterior pituitary to release ADH
ADH stimulates the collecting ducts of the kidneys, opening Aquaporins and increasing H2O reabsorption
More H2O reabsorption increases blood volume which increases BP
PTH effects on blood Ca2+ levels
The parathyroid gland produces PTH, which goes from the blood to the bones, causing Ca2+ release into the blood
PTH causes the kidneys to reabsorb Ca2+
PTH promotes the activation of Vitamin D in the kidneys, increasing Ca2+ absorption from food
Sweating and H2O Volume
Water loss occurs through sweating
Sweat glands obtain water from capillary filtration
As filtration occurs, blood volume and pressure drop, and concentration rises
Tissue fluids are reabsorbed into the blood to replace the lost sweat
Intracellular fluid diffuses out of the cells to replace the lost tissue fluid
Fluid Intake & Kidney Function
1-3L of H2O are needed for kidneys to properly function
Drinking less than 1L/day will lower blood volume
Drinking more than 3L/day will cause frequent urination and larger amounts of Na+ to be lost, leading to osmotic shock
What is the normal pH range of blood and tissue fluid?
7.35-7.45
Metabolism constantly produces acid (Lactic acid, Phosphoric acid, Nucleic acid, Fatty acid, and Carbonic acid)
Physiological Buffer
A body system that controls the output of acids, bases, or CO2
The Urinary System buffers the greatest quantity of acid or base
The Respiratory System buffers quicker than the urinary system but has less of an effect
Chemical Buffer
A substance that binds to H+ and removes it from a solution as its concentration begins to rise or that releases H+ into a solution as its concentration falls
Bicarbonate Buffer System
Phosphate Buffer System
Protein Buffer System
Bicarbonate Buffer System
A solution of Carbonic Acid and Bicarbonate ions
The ions in this solution participate in a reversible reaction where HCO3- binds to H+ to raise pH or it releases H+ to lower pH
Phosphate Buffer System
A solution of Hydrogen Phosphate and Dihydrogen Phosphate
This solution plays an important role in buffering the ICF and Renal Tubules
Protein Buffer System
The protein buffer system accounts for 75% of all chemical buffering in the body fluids
The side groups of proteins allow them to effectively pick up and release H+
Respiratory Control of pH
The Bicarbonate Buffer system is the basis for respiratory control over pH
Respiratory Control can neutralize 2-3x as much acid as the chemical buffers can
What happens if pH changes too drastically?
Altering pH too far one way or the other will drastically alter the shape and function of proteins
Damaged proteins cannot regrow or recover
Stages of Digestion (5)
Ingestion: Selective intake of food
Digestion: Mechanical & Chemical breakdown of food into usable form
Absorption: Uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and lymph
Compaction: Absorbing H2O and consolidating the ingestible residues into feces
Defecation: Elimination of feces
Mechanical vs. Chemical Digestion
Mechanical Digestion: The physical breakdown of food via mastication and the churning action of the stomach and intestines. This churning exposes more surface area of the food to digestive enzymes
Chemical Digestion: Hydrolysis reactions that break dietary macromolecules into monomers.
Parts of the Digestive Tract in order
Mouth
Pharynx
Esophagus
Stomach
Small Intestine: Duodenum, Jejunum, Ileum
Large Intestine: Cecum, Ascending, Transverse, Descending Colon, Sigmoid Colon, Rectum, Anal Canal, Anus
Accessory Organs of the Digestive Tract
Teeth, tongue, salivary glands, liver, gallbladder, and pancreas
Types of Tongue Muscles
Intrinsic: Help with subtle tongue movements for speech
Extrinsic: Produce stronger movements for food manipulation
Types of Teeth
Incisors: Used for chopping/clipping foods like carrots
Canines: Used for tearing tougher foods like meat
Molars: Used for crushing and grinding foods
Enamel
The hardest substance in the human body coats the crown portion of each tooth. It cannot regrow
Dentin
The yellowish living tissue underneath the enamel. It can restore itself
Gingival Sulcus
The groove between gums and teeth where they connect
Cementum
“Glue” that holds the tooth roots in place
Root Canal
Houses nerves and blood vessels in the roots
Pulp Cavity
Houses nerves and pulp. Tooth pain comes from this region
Periodontal Ligament
Connects the mandible to the bones of the teeth
Plaque
Sticky residue on the teeth that is made of bacteria and sugars
Once calcified, it becomes calculus
The bacteria metabolizes the sugars and produces acid, which causes cavities
Solutes found in Saliva
Amylase: digests starch and begins working in the mouth
Lingual Lipase: digests fat and begins working in the stomach
Mucus: binds and lubricates food, aids in swallowing
Lysozyme: an enzyme that kills bacteria
Immunoglobulin A: an antibody that slows bacterial growth
Electrolytes: Na+, K+, Cl-, phosphate, and bicarbonate
The pH of saliva is between 6.8-7.0
Intrinsic Salivary Glands
Small glands that secrete saliva at all times
Extrinsic Salivary Glands
Large glands that produce saliva in response to food
Parotid, Submandibular, and Sublingual glands
Swallowing (Deglutition) Phases
Oral Phase: Under voluntary control, the tongue presses against the palate, forming a bolus and pushing it back to the pharynx. The epiglottis tips posteriorly and the bolus slides around it into the laryngopharynx
Pharyngeal Phase: Under involuntary control, the palate, tongue, vocal cords, and epiglottis block the oral and nasal cavities while the bolus passes into the esophagus
Esophageal Phase: Peristalsis contractions occur, pushing the bolus through the esophagus into the stomach where the bolus becomes chyme
Digestion in the Stomach
The stomach churns to mechanically break up food. As the food liquefies, proteins and fats begin to be digested
Pyloric Sphincter
A ring of smooth muscle around the bottom of the stomach that controls the release of contents into the small intestine
Mucosa of the Stomach Wall
Mucous Cells: Secrete Mucus
Regenerative Cells: Sit at the base of each gastric pit and divide rapidly to replace dead cells
Parietal Cells: Secrete hydrochloric acid and intrinsic factor. Their shape allows for more secretion
Chief Cells: Secrete gastric lipase and pepsinogen for the breakdown of proteins and fats
Enteroendocrine Cells: Secrete hormones and paracrine messengers that regulate digestion
Functions of Hydrochloric Acid and Pepsin in the stomach
HCl kills bacteria and helps to break down proteins
When mixed with pepsinogen, HCl cleaves a peptide from it, leaving Pepsin
Pepsin can digest proteins and aid in further peptide removal
What Causes HCl Production
Stomach stretching can stimulate HCl production. The more full the stomach is, the more HCl is secreted
Phases of Gastric Function Regulation (3)
Cephalic Phase: The brain is involved, causing the stomach to respond to sight, smell, taste, or the thought of food, leading to stomach secretions
Gastric Phase: Ingested food stretches the stomach and increases the pH of the stomach contents, causing secretion
Intestinal Phase: The duodenum responds to arriving chyme and moderates gastric activity via hormones and nervous reflexes
Liver and Gallbladder (Bile) function
The Liver produces bile, which is then stored in the gallbladder where it becomes more concentrated
Bile is a salt that breaks down fats through emulsification
