Fluid balance and composition

• The brain and kidneys have the highest water proportions, comprising 80–85% of their masses.

Fluid Compartments

• Intracellular fluid is the fluid within cells, holding most of the body's water.
• Interstitial fluid is part of the extracellular fluid located between cells, excluding blood plasma.

Body Fluid Composition

• Blood plasma has a high concentration of sodium, chloride, bicarbonate, and protein.
• Interstitial fluid contains high concentrations of sodium chloride and bicarbonate, but lower protein levels.

Types of Solutes

• Electrolytes are substances with chemical bonds that allow them to dissociate into ions in a solution. carry an electrical charge and are crucial for fluid balance; sodium chloride is an example.
• Non-electrolyte organic substances- these have chemical bonds that do not allow them to dissociate in a solution; glucose is an example

Water Intake

• Water enters the body through food, liquids, and cellular metabolism.

Water Excretion

• Water leaves the body via urine, respiration, sweat, and feces.

Fluid Balance Principles

• Fluid balance is maintained only when input equals output.
• Fluid balance mechanisms sustain normal blood volume, potentially at the expense of interstitial fluid volume.

Water Movement Control

• Rapid fluid balance adjustments occur through water movement control between intracellular and extracellular fluid compartments.

Total Water Volume

• Homeostasis of total water volume is primarily maintained by adjusting urine volume and secondarily by fluid intake.

Urine Volume

• An increase in urine volume leads to a decrease in blood volume, and vice versa.

Capillary Hydrostatic Pressure

• Net filtration, the movement of fluid out, occurs at the arterial end of capillaries where capillary hydrostatic pressure exceeds blood pressure.
• Net reabsorption, the movement of fluid in, takes place at the venous end.

Hydrostatic Pressure

• Hydrostatic pressure is the force exerted by a fluid against a wall and is generally lower in venous systems and higher in arterial systems.
• Increased hydrostatic pressure in the kidneys elevates the amount of water leaving the capillaries.

Facilitated Diffusion

• Glucose molecules use facilitated diffusion to move down a concentration gradient, facilitated by carrier protein channels.

Pressure Types

• Hydrostatic pressure is the force that pushes fluid out.
• Osmotic pressure retains fluid within a container.
• Net filtration pressure is the sum of osmotic and hydrostatic pressures.

Intracellular Fluid

• Water and electrolyte levels are regulated, and the lipid bilayer separates intracellular and extracellular fluid.
• Unequal concentration on either side of the bilayer can cause electrical charge differences.

Sodium-Potassium Pump

• The sodium-potassium pump uses ATP to transfer sodium out of the cytoplasm into extracellular fluid and potassium in the opposite direction.

Interstitial Fluid Hydrostatic Pressure (IFHP)

• IFHP is generated by water in the interstitial fluid.

Blood Hydrostatic Pressure (BHP)

• BHP is generated by water inside the capillaries and is higher at the arterial end.

Blood Colloid Osmotic Pressure (BCOP)

• BCOP is largely generated by plasma proteins, which retain water.

Interstitial Fluid Colloid Osmotic Pressure (IFCOP)

• IFCOP is almost 0 mmHg, usually due to a lack of proteins.

Edema

• Allergic reactions can cause capillaries to leak excess fluid, leading to edema.

Renin-Angiotensin-Aldosterone System

• The renin-angiotensin-aldosterone system is crucial for fluid balance.

Thirst Response

• Osmoreceptors detect decreases in water levels and angiotensin II helps stimulate thirst.

Osmolality

• Osmolality is the concentration of solutes.

Antidiuretic Hormone (ADH)

• Also known as vasopressin, it is produced in the hypothalamus and released by the posterior pituitary.

Roles of ADH

• ADH causes the kidneys to retain water and is released by osmoreceptors in the brain.
• It constructs arterioles in the peripheral circulation, reducing blood flow to extremities and increasing blood supply to the core of the body.
• ADH causes epithelial cells lining renal collecting tubules to move water channel proteins, known as Aquaporins, from the interior of cells to the apical surface.

Outcomes of ADH

• ADH leads to increased water reabsorption and increased blood volume.

Diuretics

• A diuretic increases urine output, decreasing water conservation by the body.

Aldosterone Feedback Loop

• Aldosterone is released by the adrenal gland when potassium increases or sodium decreases.
• It enhances the reabsorption of sodium and water and acts on the distal tubules.

Angiotensin II

• Angiotensin II stimulates the release of aldosterone from the adrenal cortex and causes vasoconstriction, leading to increased blood pressure.
• It activates the sodium/potassium pump in the distal convoluted tubules and collecting ducts.

Kidneys

• The kidneys process incoming blood plasma to produce urine and maintain homeostasis.
• They play a role in fluid and electrolyte balance, with nephrons as the functional units that stimulate sodium ions and water reabsorption, where urine is produced.

Renal Structures

• The renal artery feeds each kidney, carrying oxygenated blood.
• The renal vein carries deoxygenated blood to and from the kidneys.
• The ureter carries all urine to the bladder.
• The renal cortex is the outer layer, and the renal medulla is the inner layer composed of calluses/pelvis.
• The minor calyx leads to the ureters.

Bladder Layers

• The outer layer of the bladder is the outer.
• The middle layer consists of two layers of smooth muscles (urine → urethra).
• The inner layer has an epithelium with folds and a mucus lining.

Urine Flow

• Urine flows from the nephrons to the collecting ducts, then to the minor calyx which leads to major calyx, into the renal pelvis, through the ureter, into the bladder (reservoir), and finally out through the urethra to the external environment.

Blood Flow in the Kidneys

• Blood flows via the abdominal aorta to the renal artery, then to the segmental arteries, lobar arteries, interlobular arteries, arcuate arteries, and afferent arterioles.
• Blood passes through glomerular capillaries (the first part of the nephron), then to efferent arterioles, and peritubular capillaries around the tubules and vasa recta.
• It returns to the heart via the venous system, following the reverse path as the arteries.

Glomerulus

• The glomerulus is where the capillary bed filters blood, captured by the Bowman's capsule.

Micturition (Urination)

• Micturition involves an increase in bladder volume causing an increase in internal bladder pressure.
• This activates mechanoreceptors (stretch-like) and a parasympathetic reflex.
• The reflex starts contractions of the detrusor smooth muscles in the bladder and relaxes the internal urethral sphincter (involuntary control).
• The external urethral sphincter muscle (voluntary control) first contracts and then relaxes, leading to the release of urine.

Urethral Sphincters

• The internal urethral sphincter is made of smooth muscle under involuntary control, regulated by the autonomic nervous system.
• The external urethral sphincter is skeletal muscle under voluntary control.

Urinary System

• The urinary bladder serves as a reservoir for urine and has a triple layer of smooth muscle (detrusor muscle).
• The ureters carry urine from the kidney to the bladder.
• The urethra transports urine from the bladder out of the body and is shorter in females and longer in males.

Peristaltic Contractions

• Peristaltic contractions help move urine through the lumen with fluid pressure and gravity.

Renal Hilum

• The renal hilum is the entry and exit site for structures servicing the kidneys.

Nephron Parts

• The renal corpuscle, composed of the glomerulus and Bowman's capsule (which filters blood), is central.
• The renal tubule is the area where secretion and absorption occur, extending from the capsule and consisting of three segments.

Renal Tubule Segments

• The proximal convoluted tubule is responsible for the greatest absorption and secretion.
• The nephron loop (loop of Henle), and the distal convoluted tubule also play parts in this process.

Podocytes

• These maintain the glomerular filtration barrier and interlock with pedicels.

Fenestrated Capillary

• It allows many substances to diffuse from the blood while preventing the passage of large elements.

Renal Circulation

• Blood passes through the renal corpuscle, then the capillaries form a second arteriole (efferent arteriole).
• The capillary network around distal portions of the nephron tubule (peritubular capillaries and vasa recta) is created and blood then returns to the venous system.

Reabsorption Modes

• Sodium ions are actively transported via a Na+ ATP pump.
• Chloride, phosphate, and bicarbonate ions undergo passive transport due to electrical charge imbalances caused by Na+ movement.
• Water undergoes passive transport due to osmotic imbalances caused by Na+ and Cl- movement.
• Glucose and amino acids are passively transported by sodium cotransport mechanisms, and urea is also passively transported.

Countercurrent Multiplier System

• Na+ and Cl- are reabsorbed into the interstitial fluid via active transport in the ascending loop; wall thickness prevents return of Na+ and Cl- to the tubule.
• Tubular fluid is diluted, and osmotic pressure in the interstitial fluid increases.
• High interstitial fluid osmotic pressure causes passive movement of water out of the descending loop into the interstitial fluid and then blood, because it is permeable

Urea

• Diffuses from interstitial fluid into the tubule in the descending limb, increasing osmotic pressure in the descending limb as it enters the medulla.

Ion Reabsorption

• Sodium and potassium ions, through active transport, are reabsorbed into the interstitial fluid in the ascending loop.

Interstitial Fluid Osmotic Pressure

• High interstitial fluid osmotic pressure causes the passive movement of water out of the descending loop of Henle, which features aquaporins.
• This countercurrent multiplier system operates in a parallel process where flow occurs in opposite directions.

Loop of Henle

• In the descending and ascending portions of the loop of the nephron, water exits and urea enters passively at the descending limb.

Cell Channels

• A principal cell possesses channels for the recovery or loss of sodium and potassium.
• An intercalated cell secretes or absorbs acid or bicarbonate.

Collecting Ducts

• ADH stimulates cells to insert aquaporins here.
• This allows for the recovery of large amounts of water from the filtrate back into the blood.
• When ADH is absent, water is excreted in urine.

Tubular Secretion

• Aldosterone aids in the sodium-potassium ATP pump, allowing potassium to enter the renal tubules and sodium to be pumped out.

Juxtaglomerular Apparatus (JGA)

• The JGA is on the outside of the Bowman's capsule/glomerulus consisting of macula densa cells and juxtaglomerular cells
• Macula densa cells are chemoreceptors in the distal convoluted tubule that detect sodium concentration and regulate renin release from juxtaglomerular cells.
• Juxtaglomerular cells are mechanical receptors near the afferent arteriole that are responsible for detecting stretch.

Hormonal Regulation

• ADH is an antidiuretic hormone that helps retain fluid.
• RAAS increases sodium reabsorption in the distal convoluted tubule, increasing blood volume and decreasing urine.
• ANH promotes sodium loss in the urine, decreasing water reabsorption and opposing the action of ADH/RAAS, decreasing blood volume and increasing urine.
• Urine consists of 95% water, with nitrogenous wastes from protein metabolism.

Urine Composition

• Electrolytes, toxins, pigments, and hormones can also be found in urine.

Urine Color

• The color of urine is determined mostly by the breakdown products of red blood cell destruction.
• Severe dehydration or renal disease results in oliguria.
• Absence of urine production is anuria.
• Excessive urine production is polyuria.

Urine pH

• Acidic urine has a pH less than 7.4 while basic urine has a pH greater than 7.4. Normal urine pH is 7.4.

Buffer Systems

• Buffer systems respond to maintain acid-base homeostasis in the body.
• Chemical buffer systems provide an immediate response.
• Physiological buffer systems, including respiratory and renal responses, take minutes to hours.

Chemical Buffer

• Chemical buffer systems shift to the left if too acidic and to the right if too basic.

Physiological Buffer Systems

• Disturbance in acid and base balance is diagnosed by a blood test.
• Acidosis indicates too much acid is above 7.48.
• Alkalosis, on the other hand, indicates too much base is below 7.48.

Acidosis and Alkalosis

• Acidosis is detected by carotid chemoreceptors that use CO2 receptors.
• The brain receives a signal to cause hyperventilation, increasing the loss of CO2, increasing blood pH increase back to normal levels.

Hyperventilation

• Prolonged hyperventilation may increase blood pH to produce alkalosis.

Acidosis Examples

• Metabolic acidosis occurs when there is too little bicarbonate in the blood.
• Respiratory acidosis is indicated through carbonic acid “too much CO2.

Alkalosis Examples

• Metabolic alkalosis occurs when there is too much bicarbonate in the blood.
• Respiratory alkalosis occurs due to a deficiency in carbonic acid.

Renal Response Steps

• Ammonia is formed by the metabolism of amino acids.
• Ammonia combines with Hydrogen to form ammonia ion.
• Ammonia ions displaces sodium to form ammonium salt which is excreted in urine
• Sodium combines with bicarbonate to form basic salt which is reabsorbed back into the blood

pH Control

• A decrease in blood pH causes carbon dioxide to diffuse from tubule capillaries into distal convoluted tubule (DCT) cells.
• Carbonic anhydrase combines carbon dioxide with water.
• Hydrogen move into urine to displace basic ions which are eliminated in urine.
• Sodium combined with bicarbonate to form sodium bicarbonate, which is reabsorbed into the blood by diffusion

Chloride

• Chloride ions are important for neutralizing positive charges in the body. If lost bicarbonate ions are used instead
• Arterial blood gas analysis provides information about a patient's respiratory status and acid base homeostasis.
• Abnormal acid levels can occur through digestive and urinary system failing to maintain proper levels (metabolic acidosis)
• Lungs fail to remove excess CO2 during normal breathing. (respiratory acidosis)

Blood Levels

• Hypercapnia causes elevated blood levels or Co2.
• Hypocapnia leads to low blood levels of Co2.
• Acid-base balance disorders can occur through diabetic acidosis or ketoacidosis, or occurs most frequently in people with poorly controlled diabetes mellitus
• When certain tissues in the body cannot get adequate amounts of glucose, they depend on the breakdown of fatty acids for energy.

Key Terms

• A fluid compartment is a system of fluid inside all cells of the body constitutes a compartment system that is largely segregated from other systems.
• Interstitial fluid (IF) is fluid in the small spaces between cells not contained within blood vessels
• Intracellular fluid (ICF) is fluid in the cytosol of cells
• Plasma osmolality is the ratio of solutes to a volume of solvent in the plasma. Plasma osmolality reflects a person's state of hydration.

Digestion System

• The alimentary canal is the digestive tract, including the mouth, pharynx, esophagus, stomach, small and large intestine.
• Digestion is facilitated by the enteric nervous system. The accessory organs for digestion include the liver, pancreas, and gallbladder.

Accessory Organs

• Accessory organs assist with digestion.

Digestion Steps

• Ingestion involves taking food into the mouth, followed by propulsion, where it's swallowed.
• Mechanical digestion includes chewing and churning, along with segmentation for mixing contents in the small intestine.
• Chemical digestion breaks down large food molecules into building blocks.
• Absorption transfers nutrients and water into blood and lymph vessels, primarily in the small intestine.
• Defecation excretes waste through the anus.

Sphincters

• Sphincters regulate passage in digestive system.
• The anal sphincter controls the exit at the rectum while the ileocecal valve controls entry of the small intestine (ileum) --> large intestine (cecum). The lower esophageal sphincter prevents backflow from the esophagus to the stomach
• Pyloric Sphincter connect Stomach → duodenum (small intestine)
• Upper Esophageal Sphincter connect Pharynx → esophagus.

Nerve Plexuses

• Extrinsic nerve plexuses use long reflexes involving the autonomic nervous systems to external stimuli.
• Intrinsic nerve plexuses use short reflexes within the alimentary canal wall

Hormonal Control

• Gastrin is a digestive hormone of the stomach, stimulated by food, and it stimulates parietal cells to secrete gastric acid.

GI Hormones

• GI hormones are produced and act upon the gut (accessory organ), secreted by specialized epithelial cells (called endocrinocytes). They go through bloodstream

Secretin

• Produced by the duodenum
• stimulates the secretion of pancreatic enzymes and bile from liver; cholecystokinin (CCK) Stimulates a watery secretion of bicarbonate from pancreas.

Peristalsis

• Peristalsis is the movement of food through the digestive tract via repeating motion.

Segmentation

• Segmentation, which occurs mostly inside the small intestine, separates chyme.

Alimentary Layers

• Layers of the alimentary canal consist of the serosa which is a visceral layer that covers organs, anchors the gut to the abdominal cavity, is continuous with the mesentery, and secretes fluid to reduce friction
• Muscularis has two smooth muscle layers (myenteric plexus) for peristalsi
• adventitia is a sheath of collagen fibers (covers mouth, pharynx and esophagus).

Submucosa

• Submucosa is an exocrine glands, blood vessels, lymphatic vessels (controlled by submucosal plexus.
• It supports the mucosa, provides a vascular network, and facilitates nutrient absorption and defense.

Mucosa

• Mucosa has three layers: mucosal epithelium, lamina propria, and a muscularis mucosa. The simple epithelium facilitate absorption/secretion mainly found in stomach and intestines
• Protects against wear and tear from Stratified squamous epithelium and is on mouth, pharynx, analis only layer involved in contact with digested food and monitors contents by receptors.

Peritoneum

• The peritoneum is a sheet in the abdominal cavity that holds digestive organs in place
• Parietal peritoneum lines the abdominal wall
• Visceral peritoneum envelopes the abdominal organs

Nervous System

• The nervous system has Peripheral and System parts
• Peripheral Nervous System has Autonomic and Somatic Parts
• Atonomic Nervous System has: Sympathetic, Parasympathetic, Enteric

Swallowing

• Deglutition which has three phases: oral, pharyngeal, and esophageal.
• Oral under voluntary, pharyngeal- in voluntary- smooth muscle. Esophageal also smooth musle

Chewing

• Also known as mastication

Saliva

• Consists of mucus, enzymes, and water
• (amylase) and to help with PH we use (sodium bicarbonate

Bolus

Rounded mass of food that is mixed with saliva

• Submandibular: glands: in the floor of the mouth
• Sublingual: below the tongue

Parotid glands

• Lie between the skin and the masseter muscle, near the ears.
• Secrete saliva into the mouth through the parotid duct, which is located near the second upper molar tooth

Esophagus

• Upper: controls the movement through movement .- Lower controls movement from it to the stomach

The 4 regions of the stomach

• Cards= connect to esophagus to stomach
• Stomach releases the gastrin, ghrelin

Histology in stomach:

• HydroCloric acid- created by parietal cells
• The chief cells: secrete pepsinogen. _The mucos: secrete acidic mucus
• Enderocrine: secrete horomones and gastrin

Gastric Phase

• cephalic is from smell/ taste
• gastric phase is from basic and gastric
• Intestinal Phase is intestine of chime

Small intestine

• Duodeum, jejunem, lieum- (longest part) most water is reabsorbed here
• Digestion is complted
• circular fold

Large intestine

• Absorbs water
• history
• gobel cells

Histology in large intestine

• No circular fold
• Mucosa has: enterocyts, and gobelt cells

Liver

• largest, produces bile
• bile delievers to the common hepactic duct
• Breaksdown LARGE INTO SMALL( fat) bile controlled Cholestokinin (CCK

Bile

• liver, cystic duct, galbladder, small/duodeum

Bilirubin

• the main bile pigment, is a waste product produced when the spleen removes old or damaged red blood cells from the circulation.

Sinusoid

• Sinusoid open porous blood
• Retiuculoenedial remove blood cells.

Triad portal

• interloblar: transport oxygen
• interlobulore: transport nutrien
• interloblar: to heaptic duct

Galbladder

• Bile
• Soduim Bicarbonte increase with higher pH
• Breaks down fat

Pancreas

• produce digestive enzymes and pancreatic juices
• exocrine contains digestionzmes produce and
• endocrine islet, insulin glucagon hormones

Digetsive emzyme

• Digests starches, fates, proteins Tripcase breaks down protein Enzyme by intestinal mucos is enterkinase

Absorption

water is osmosis, for water glucose is cupled sodium is secondary active

2 parts for Absorption

• mono acds, absorbed into blood to liver,
• Fat absorb to lyphms

Carbohydrates

• Brush border enzymn dextrise strarts working on off glucose
• Lipids: transforms as absorp to pethelial cells
• Mecilli: forned a sperical cells by lipe hydrolize.