• functional units of respiration take up most of the area in interpulmonary space
• air-filled sacs
• 2 types

• Type I: Epithelial cells, provide structural support
• Type II: Septal cell, produce surfactant

• Carry O2 to tissues
• Bring CO2 to lungs for excretion

• Process of inspiration/expiration
• Amount of air inhaled/exhaled is determined by several Gas Laws

• sum of partial pressures adds to total pressure PT = (%N2 * PT) + (%O2 * PT) + (%CO2 * PT) + etc…
• %O2 = 21%

• pressure inside the lungs
• Must be negative to allow inspiration
• Boyle’s Law

• pressure inside the pleural cavity
• Always negative
• Keeps lungs inflated

• PASSIVE PROCESS!!! No muscles necessary for normal quiet expiration
• Intrapulmonary Pressure: Becomes positive to exhale air
• Intrapleural Pressure: Remains negative to keep lungs inflated; Less negative than during inspiration

Spirometry

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Measurements of lung volumes

a. Inspiratory reserve volume
b. Vital capacity
c. Inspiratory capacity
d. Tidal volume
e. Expiratory reserve volume
f. Total lung capacity
g. Residual volume
h. Functional residual capacity

• air in the conducting zone
• DS = TV - alveolar volume

• Occurs in alveoli at the respiratory membrane (alveolar-capillary)
• Brings O2 in, CO2 out

• Type I alveolar cells and associated basement membrane
• Endothelial cells of pulmonary capillaries and associated basement membrane

• 1.5% dissolved in plasma
• 98.5% bound to hemoglobin

• 7-10% dissolved in plasma
• 20-30% bound to hemoglobin
• 60-70% bicarbonate ion

• Right shift of Curve due to increased H+ concentration
• Corresponds to decrease in pH
• Decreases O2 binding affinity

1. Higher brain centers
2. Joint/muscle receptors
3. Irritant/Stretch receptors
4. Emotional stimuli
5. Peripheral Chemoreceptors (carotid artery and aortic arch) Mostly CO2
6. Central Chemoreceptors (Medulla) H+

• Lung Cancer: 87% due to smoking
• Emphysema: Disease of over-compliance
• Pneumonia: Fluid in the lungs

Renal System

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• Pressures drive materials from the blood into Bowman’s capsule
• Hydrostatic pressure: 55mmHg into Bowman’s capsule
• Osmotic pressure: 30mmHg out of Bowman’s capsule (albumin concentration)
• Capsular Hydrostatic Pressure: 15mmHg out of Bowman’s Capsule
• Net Filtration Pressure: 10 mmHg into Bowman’s capsule

• Myogenic control: Smooth muscle cells tend to contract when under pressure, “Closes the valve”
• Macula densa/Juxtaglomerular Apparatus:
• Macula densa monitors salt concentration and releases adenosine in response to low salt
• Juxtaglomerular cells detect adenosine and release renin
• Renin initiates a cascade which results in constriction of efferent arteriole. Constriction leads to an increase in net filtration pressure

• Smooth muscle cells tend to contract when under pressure
• “Closes the valve”

• Macula densa monitors salt concentration and releases adenosine in response to low salt
• Juxtaglomerular cells detect adenosine and release renin
• Renin initiates a cascade which results in constriction of efferent arteriole
• Constriction leads to an increase in net filtration pressure

• 100% glucose and amino acid resorption
• Cross apical side via Na+ driven cotransporters
• Cross basilar side via passive channels 65% water and ion resorption Remember…resorption means the “reuptake” of materials into blood
• Materials leave the nephron and enter the paratubular capillary

• Important for water resorption
• Water exits through specialized water channels called aquaporins
• PASSIVE DIFFUSION occurs here
• Allowed due to the corticomedullary gradient….more later

• Resorption of salts occurs here
• Bottom of ascending limb = passive diffusion Top of ascending limb = active pumping
• Also allowed due to corticomedullary gradient

• More salt reabsorption -> hormonally controlled
• Filtrate salt concentrations here are LOW!
• Hormonal Regulation
  • Aldosterone: released from the adrenal cortex
  • Causes an increase in production and insertion of Na+ pumps and channels
  • High Aldosterone = more sodium resorption

• Incredibly low numbers of ion channels…no ion resorption
• Aquaporins are found here
  • Hormonal control: ADH (Vasopressin)
  • ADH causes more aquaporins to be created and inserted in the membrane
  • More ADH = more water resorption
• Also permeable to urea

• Within the kidney (but outside the nephron) ionic concentration increases with depth into the medulla
• This gradient is highly dependent on urea concentration
• Gradient is maintained by vasa recta
  • Vasa recta: blood vessel which has very low hydrostatic pressure
  • Ionic concentration in the blood in the vasa recta is equal to the ionic concentration in the kidney at all places!!!

• blood vessel which has very low hydrostatic pressure
• Ionic concentration in the blood in the vasa recta is equal to the ionic concentration in the kidney at all places!!!

Loop of Henle

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• Major: Esophagus, Stomach, Small intestine, Large intestine, Pancreas, Liver
• Accessory: Brain, Salivary glands

• One of the GI control systems
• Local system
• Has connections with the CNS

• One of the GI control systems
• Scattered epithelial cells throughout GI tract release hormones into blood

• 4 Major layers in each piece called “tunics”
• From outside to lumen:
  • Serosa: thin outer layer
  • Muscularis: smooth muscle layers, funtion in motility
  • Submucosa: connective tissue, blood, lymphatics
  • Mucosa: epithelial cells including endocrine cells, contact with lumen

• Includes manual processing of food (i.e. chewing and swallowing)
• Control of Food Intake
  • Hypothalamus: control of hunger drive
  • Fat cells release leptin
  • Leptin “turns off” hunger
  • Can only be used as a weight control agent in leptin deficient people

• Moves food to stomach
• Uses peristalsis for motility
• Food stays here 4-5 sec.
• Secretion of mucus
• No absorption
• Type of epithelium = stratified squamous epithelium

• Epithelial type: columnar epithelium
• 2 types of motility:
  • Relaxation
  • “Gastric Grinder”
• Secretion:
  • Pepsinogen: protease which auto-catalyzes its activation, begins protein digestion, secreted via Chief Cells
  • Acid: Sterilizes stomach contents, secreted via Parietal cells
  • Gastrin: hormone, meaning it is secreted into blood, necessary for the release of acid from parietal cell, from G cell
  • Mucus: epithelial cells

• 3 molecules need to bind parietal cells to stimulate acid secretion
  • Histamine (most common pharmaceutical target)
  • Gastrin
  • Acetylcholine
• Acid created by dissociation of carbonic acid
  • Carbonic acid created by carbonic anhydrase
  • Hydrogen ions pumped into lumen via proton pump

• Cephalic: low level secretion in response to the presence of food
• Gastric: Stomach distended when food enters
• Intestinal: Slow release of food into small intestine, distension of small intestine causes cessation of stomach secretion and motility (ENS)

• Food entering small intestine stimulates endocrine activity
• Fats and Proteins: Act on cells to initiate release of cholecystokinin (CCK)
• Acid: acts on cells to initiate release of secretin Hormones released from these small intestine endocrine cells act on the pancreas and liver

• Has both endocrine and exocrine functions
• Exocrine functions involved in digestion
  • Secretes 2 major substances into small intestine
    • Digestive enzymes
    • Bicarbonate

• Secretion is driven by CCK
• 3 types of enzymes
  • Proteases
    • Trypsinogen
    • Chymotrypsinogen
  • Amylase
    • Carbohydrate digestion
  • Lipase
    • Lipid digestion

• Trypsinogen and chymotrypsinogen are inactive forms
• Enterokinase in the small intestine activates trypsin
• Trypsin activates chymotrypsin
• Trypsin and chymotrypsin work on protein digestion

• Released in response to secretin
• Acts as a base to neutralize acid released into the small intestine from the stomach

• Aids in digestion via lipid digestion
• Receives 75% of its blood supply from the hepatic portal vein
  • Contains blood which has passed the GI tract (lots of nutrients here)
• Also receives blood from the hepatic artery
• Blood contacts liver cells (hepatocytes) via sinusoids
• Hepatocytes secrete bile
• Bile is transported through canaliculi between sheets of hepatocytes
• Canaliculi converge into the common bile duct
• The common bile duct empties into the small intestine

• 75% from Hepatatic portal vein
• Hepatatic artery

• Hepatocytes
• Sinusoids
• Bile

• Transports bile
• Converge into the common bile duct which empties into the small intestine

• breaking up blobs of lipid into smaller water soluble blobs called micelles
• Bile acids aid lipase in lipid digestion

• Most nutrient absorption occurs here
• Absorptive epithelial cells transport nutrients from the lumen to the blood stream
• These cells reside on the tips of villi
• Villi create folds in the small intestine
• The bottoms of these folds are called crypts
  • Stem cells in the crypts divide to make more absorptive epithelial cells

• Folds in the small intestine
• Dips are called crypts
• Epithelial cells on tips

• Apical region of mature absorptive epithelia
• Contains membrane bound enzymes which finish digestion
  • Peptidases convert peptides to amino acids
  • Lactase converts lactose to glucose and galactose

• Polysaccharides are broken down by amylase in the lumen
• Brush border enzymes break disaccharides into monosaccharides
• Sodium in the lumen binds hexose transporter
• Glucose also binds transporter and both molecules are transported across the membrane
• Glucose diffuses passively out the basilar side of the cell and into the blood stream

• Osmotic gradient must be created to shuttle water into the blood stream
• Sodium flows into epithelial cells creating this osmotic gradient
• Water then passively flows through the cell and into the blood

• Process is nearly the same as that for glucose
  • Utilizes peptidases in the brush border
  • Utilizes a Na+ driven cotransporter for amino acids

• Triglycerides are broken down in the lumen by lipase and bile acids
• Monoglycerides and fatty acids freely diffuse through the membrane of the absorptive epithelium
• MGs and FAs conglomerate into chylomicrons
• Golgi apparatus packages chylomicrons for exocytosis
• Chylomicrons then diffuse to the central lacteal

• Final water and salt absorption
• Creation of feces for defecation
• Contains millions of microbes (lots of E. coli)
• Fermentation:
  • microbes utilize carbohydrates.
  • Microbes contain cellulases which can break down cellulose (normal digestion does not break down any cellulose)

• Objective: Maintain blood glucose levels in a normal range
• Controlled by endocrine hormones which trigger biochemical processes
• Processes
  • Glycogenesis
  • Glycogenolysis
  • Gluconeogenesis
  • Glycolysis
  • Krebs cycle and Oxidative Phosphorylation