Module 3 - GIT and renal Flashcards
Two forms of digestion:
Digestion
* Physical: the physical break down of food into smaller particles via processes like chewing, biting, and mastication
* Chemical: uses digestive enzymes to further break down these molecules, allowing absorption by the body, which occurs mainly in the stomach and small intestine
GIT Consists of
- Alimentary canal and accessory glands that secrete digestive juices into the canal through the ducts
- Comprised of: Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus
Peristalsis
a series of wave-like muscle contractions that move food through the digestive tract
Sphincters
Close like drawstrings which open or close the tube when required
Three Accessory glands
Salivary, pancreas, liver
Foregut
from the oral cavity to the initial part of the
duodenum (Celiac trunk)
Midgut
from the duodenum to the initial two-thirds of the
transverse colon (Supmesenteric artery)
Hindgut
from the later one third transverse colon to the
upper portion of the anus (Infmesenteric artery)
Oral cavity
- Site for: Physical (teeth) and chemical (amylase)
digestion - Chemical digestion: Saliva (mucin, buffers (HCO3, antibacterial); 1.5L/day, pH= 7 or slightly above, Amylase; Action: Hydrolyses starch and glycogen to
smaller poly-saccharides and maltose - Tongue: Taste buds and food bolus
Oesophagus
- Conducting pathway
- Top muscle coat striated
(voluntary) - Remaining bit smooth
(involuntary)
Pharynx
- Fork in the road- opens to both digestive and respiratory
passages - Respiratory passages are closed
during swallowing - If swallowed material goes down
into the respiratory passage
cough (protective) or choking (fatal)
Stomach
- Reservoir ~2.5L
- Location: upper (L) abdomen
- Important functions
- Gastric juice and smooth
muscles help digestion further - Gastric juice- Acid (pH (2)) and
Pepsin - Primary meat and plant
material digestion and
secondary kills bacteria - Pepsin- hydrolyzes proteins
- Mucus
Liver
- Size ~2Kg
- Location: upper abdomen
- Porta hepatis and portal triad
- Functions
- Bile production
- Storage
- Nutrient interconversion
- Detoxification and first-pass
- Phagocytosis and
- Synthesis
Spleen
- “to act as a filter for blood. It
recognizes and removes old,
malformed, or damaged red
blood cells. Spleen performs
quality control”.
Pancreas
- Close to duodenum
- Mixed gland
- Acini
- Islet of Langerhans
Small intestine
- Whopping ~6m in length
- 3 components: the duodenum, jejunum, and ileum. Duodenum- 25cm long, chyme mixes with bile and pancreatic juice, Jejunum-4m long, absorption (AA, Lipids, CHOs, Fe and Ca2+ and Ileum-2.5m long, B12 and bile salts absorption
- 3 Functions:
1. Motility
2. Segmentation
3. MMC (cyclic, recurring motility pattern that occurs in the stomach and small bowel during fasting)
Rectum and anus
- The rectum is a chamber that
begins at the end of the large
intestine, immediately following
the sigmoid colon, and ends at
the anus - Eventually, the descending colon
becomes full, and stool passes
into the rectum, causing an urge
to move the bowels (defecate) - The anus is the opening at the far end of the digestive tract
through which stool leaves the
body
Large intestine
the large intestine is responsible for processing indigestible food material and is divided into four parts:
1. the cecum and ascending colon,
2. transverse colon,
3. descending colon,
4. sigmoid colon.
The large intestine performs three primary functions: absorbing water and electrolytes, producing and absorbing vitamins, and forming and propelling feces toward the rectum for elimination. The wall of the large intestine has the same types of tissue that are found in other parts of the digestive system.
Upper GIT
mouth, pharynx, esophagus, and stomach
Lower GIT
Small and large intestine, rectum, and anus
Boundary between the upper and lower GIT
Ligament of Trietz
Layers of the GIT
- Mucosa: Epithelium, Lamina propria, Muscularis mucosa
- Submucosa: Blood vessels, Meissner’s plexus
- Muscularis mucosa: Myenteric plexus, Longitudinal muscle
- Adventitia: Connective tissue and variable amount of adipose tissue
Ingestion
the process by which food is taken into the alimentary canal. It involves chewing and swallowing
Propulsion
Movement of food through the GIT
Segmentation
occurs mainly in the small intestine, consists of localized contractions of circular muscle of the GI tract
ANATOMY OF THE ORAL CAVITY
- Mouth: Vestibule and oral cavity proper, Palate
- Teeth
- Types:
- Incisors
- Canines
- Premolars
- Molars
- Formula: Child (2,1,2,0)x4 * Adult (2, 1, 2, 3)x4
- Tongue: Taste buds (Filiform, Fungiform, Foliate, Circumvallate)
- Salivary glands: Parotid (25%, Serous, Amylase), Submandibular (70%, mixed, lysozyme and lactoperoxidase), Sublingual (5%, mucous, lingual lipase
TASTE PATHWAYS
- 3 cranial nerves
- 7th, 9th and 10th cranial nerves
- Medulla
- Thalamus and
- Gustatory centre in cerebral cortex
CONTROL OF SALIVARY SECRETIONS
PARASYMPATHETIC- ACH (M3) AND NORADRENALINE (⍺-ADR) ACTIVATE THE PIP2 PATHWAY → CA2+ AND CL- CHANNELS- WATERY SALIVA
SYMPATHETIC- Β-ADR ACTIVATION LEADS TO RELEASE OF ENZYMES- MUCUS
DEFECATION REFLEX
- colon muscles contract to move the stool towards the rectum, and the rectal walls expand with filling, stimulating the desire to defecate
- The defecation reflex pathway is triggered when the rectum is distended, and a series of reflexes take place that lead to the relaxation of the external sphincter, contraction of abdominal wall muscles, and relaxation of pelvic wall muscles.
THE STOMACH AND
ITS CELLS
Role: Storage, motility, mechanical breakdown
Cells: pepsin, HCL, neurohormonal reflex, antiseptic cephalo- and gastrogastric reflexes
MMC
Migrating motor complex (MMC) is a mechanical and chemical cleansing of the empty stomach in preparation for the next meal.
Role of MMC
- Mixing peristaltic waves
- Gastric emptying
- 1mm3 and exit volume of 5mL
- Vomiting
- Causes: metabolic conditions and drugs
- Activation of vomiting center in the medulla, CTZ inner parts of cerebral cortex
Gastric secretions
- Mucus
- Prostaglandins
gastric acid secretion
- UptakeofCO2,Cl-,Na+andwater
- Active secrete HCl into the lumen of the stomach (ACH, Gastrin, Histamine)
- HCO3- into the blood
- Role of H+/K+ -ATPase antiporters
- Alkalinetide
control of gastric secretion
Primary activators
* 10th nerve, gastrin and histamine*
Primary inhibitors
* Secretin and somatostatin
* Regulation: Cephalic, Gastric, Intestinal
ROUTES OF CELLULAR ABSORPTION
- ATP energy source
- Transcellular
- Paracellular
- Water absorption against osmotic gradient
CONTROL OF BILE SECRETION
- Secretin from duodenum
- Role of CCK
- 10th nerve stimulation
- Positive feedback
CONTROL OF PANCREATIC SECRETION
Stimulation via CCK
* Secretion plus relaxation of sphincters
10th nerve
CCK
The gastrointestinal peptide cholecystokinin (CCK) causes the release of pancreatic digestive enzymes and growth of the normal pancreas
Macronutrients
- Carbs are the major source of energy intake
- Reducing sugars: Glucose, fructose, galactose
- Disaccharides: Sucrose (glucose+fructose), lactose ®
(galactose+glucose) and maltose ® (2 glucose) - Starch (amylose+amylopectin)
- Glycogen (branched polysaccharides)
CARBOHYDRATE ABSORPTION
- Dietary polysaccharide conversion
- Disaccharides in the brush border
- Na+ and energy-dependent secondary active transport
- The monosaccharide fructose enters the cell by passive facilitated diffusion
- Glucose, galactose, and fructose exit the cell at the basal membrane by passive facilitated diffusion
- Simple diffusion moves monosaccharides
FAT ABSORPTION
- Triglycerides and bile
- Role of lipases
- Water soluble micelles
- Passive diffusion of fats
- Chylomicrons
PROTEIN ABSORPTION
- What does the stomach do?
- Role of amino peptidases
- Na+-andenergy-dependent secondary active transport via a symporter
- Amino acids exit the cell at the basal membrane via various passive carriers
- Amino acids enter the blood by simple diffusion
IRON ABSORPTION
- Ferrous iron
- Energy dependent transport
- Ferroprotein
- Transferrin
- Ferritin
- Lost in feces
- Unabsorbed lost in feces
Urinary system Consists of:
- 2 kidneys, which filter the blood to produce urine
- 2 ureters, which convey urine to the bladder
- Single centrally located urinary bladder, a storage organ for urine until it is eliminated, and
- urethra, which conveys urine to the exterior
Functional unit of the kidney
Nephron
What are the components of a nephron
- Glomeruli
- Tubules
Role of the Kidneys
- Remove waste products (ammonia, urea, uric acid and creatinine)
- Filter essential substances Na+ and K+
- The formation of urine (filtration, selective reabsorption and excretion)
- Endocrine function (renin and erythropoietin)
- Regulate osmolarity (measures the concentration of all chemical particles found in the fluid part of blood)
- Acid base balance (e.g., H+ vs HCO3-)
- Calcium (vitamin D to dehyrocholecalciferol) homeostasis
- Detoxification
Renal anatomy
- Retroperitoneal with variable amount of fat
- Size(♂150±25g♀135±20g)
- Fibrous capsule, Perirenal fat, Renal (perirenal) fascia and Pararenal fat
- Renal capsule
- Renal sinus
- Bean shaped
- Hilum
- Vertical extent (T12- L3/4)
- 11x6x3cms
Kidneys Internal structure
- Cortex
- Composed primarily of renal corp., PCT, DCT
- Renal columns
- Medulla
- Renal pyramids
- Consists primarily of straight tubules, Henle’s loop, CT
Renal nerve & blood supply
Sympathetic
* Renal, and superior (middle) and Inferior (lower) hypogastric plexuses
Parasympathetic
* Vagal supply via the coeliac and pelvic splanchnic nerves
Blood supply
* Renal
* Abdominal aorta * Gonadal
* Common iliac
* Internal iliac
* Vesical
* Uterine
* 20% of cardiac output via renal artery
* Vasa recta, Peritubular capillaries and Loop of Henle are involved in “counter current exchange”
Ureter nerve and blood supply
Narrowed on three sites:
Pelviureteric junction, pelvic brim and ureteric orifice
Urinary bladder and urethra
- Reservoir
- Mean capacity= ~250-300mL
- Range= 250-500ml
- Filling beyond 250mls causes a desire to micturate
- Filling up to 700ml maybe tolerated, but beyond this point it becomes painful
- Bladder: Rugae
- Urethra: Male vs Female
Nerve and blood supply of the bladder
- Vesical plexus (inferior hypogastric plexus)
- Parasympathetic (Nervi Erigentes S234): Motor to detrusor, Inhibitory to sphincter vesicae, No para no pee
- Sympathetic (T11-L2): Opposite to Parasympathetic, Somatic (S2,3,4), Voluntary to sphincter urethrae
- Pain: Spinothalamic tracts
Blood supply: Internal Iliac
Body fluids
- Total body water
- Male= 42L
- Female= 30L
- Plasma osmolality: body fluids/electrolyte balance= 275-295 mOsm/Kg
Urine contents
water (95%). The rest is urea (2%), creatinine (0.1%), uric acid (0.03%), chloride, sodium, potassium, sulphate, ammonium, phosphate and other ions and molecules in lesser amounts
Production of hyper (more) tonic (solutes) urine
Water moves out of the urine, so urine is concentrated and is called hypertonic urine
- Dehydration→ ↑ADH→ ↑aquaporin channels, CD water permeability
- More water is reabsorbed
- Urine is more concentrated
Production of hypo (less) tonic (solutes) urine
Water ingestion dilutes body fluids and reduces or stops ADH secretion; the
urine becomes hypotonic, and the extra water is excreted in the urine.
- NaCl reabsorbed by cortical CD
- Water remains in the urine
Urine formation
The process of urine formation occurs in three main steps: filtration, reabsorption, and secretion. The kidneys filter unwanted substances from the blood and produce urine to excrete them. The urine produced is mainly composed of water that has not been reabsorbed, which is the way in which the body lowers blood volume, by increasing the amount of water that is excreted.
Membrane Transport
- Simple diffusion: Simple diffusion is a type of passive transport that occurs when solutes move through a semipermeable membrane from an area of high concentration to an area of low concentration
- Facilitated diffusion: Facilitated diffusion is a type of passive transport that occurs when molecules move across a biological membrane via specific transmembrane integral proteins
- Osmosis: the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration
- Carrier mediated transport: Carrier-mediated transport is a type of transport that occurs when molecules move across a biological membrane via specific transmembrane integral proteins
Bicarbonate reabsorption
- reabsorption of one molecule of HCO3 and one molecule of Na+ from the tubular lumen into the blood stream for each molecule of H+ secreted.
- This mechanism does not lead to the net excretion of any H+ from the body as the H+ is consumed in the reaction with the filtered bicarbonate in the tubular lumen.
countercurrent multiplier system
- occurs in the loop of Henle
- the process of using energy to generate an osmotic gradient that enables you to reabsorb water from the tubular fluid and produce concentrated urine.
- This mechanism prevents from producing large quantities of dilute urine daily
loop of Henle
- U-shaped structure in the nephron of the kidney that plays a crucial role in the formation of urine.
- creates a concentration gradient in the renal medulla, which is essential for the reabsorption of water and solutes
- regulates urine volume and concentration.
Regulation of urine volume
- production of ADH
- the use of diuretics,
- need to maintain homeostasis in terms of fluid balance, solute clearance, and plasma osmolarity.
- is regulated by varying the amount of glomerular filtrate reabsorbed in different parts of the nephron.
- regulating water and sodium excretion.
Glomerular filtration rate (GFR)
- Flow of plasma from the glomerulus into Bowman’s space over a specified period and is the chief measure of kidney function
Factors that influence GFR
- Renal blood flow and perfusion
pressure - Hydrostatic pressure
- Surface area
Renal blood flow
- 1200mL/min
- Plasma= 660mL/min and 120mL/min is filtered out into the nephron
- Produce about 1.2L of urine which is 1% of filtered load
- Renal blood flow= Pressure in renal artery- pressure in renal vein
- Dependent on TRVR: SNS, adrenaline, noradrenaline, endothelin, renin, AT-II, PG, sometimes ↑ glucose and
proteins increase flow
Regulation of body fluid, osmolality and electrolyte concentration
- Tubular reabsorption
- Secretion of: Na+, K+, Ca2+, PO4-, Mg2+, Cl-, HCO3-
- Urine concentration is largely dependent of tubules
Other hormones secreted by the kidney
- Endothelins
- Potent vasoconstrictor
- Prostaglandins (PGE2, PGI2, PGF2a, PGD2, TXA2)
- Vasodilators
- Purines (adenosine and ATP)
- Vasoconstrictors
- Gluconeogenic enzymes
Urinary excretion
- For any given substance depends on GFR
- Increased by tubular secretion and reduced by tubular reabsorption
- Nitrogenous products
- Urea, creatinine, urate
Tubular reabsorption and secretion
- Capillary fluid exchange
- Filtration (very high
pressure) - Filtration
- Reabsorption – Proximal Tubule
- Reabsorption – Loop of Henle
- Reabsorption – Loop of Henle
- Secretion (Tubular excretion)
Acidosis
causes more bicarbonate to be reabsorbed from the tubular fluid, while the collecting ducts secrete more hydrogen to generate more bicarbonate, and more NH3 buffer is formed
Alkalosis
causes the kidney to excrete more bicarbonate as
there is a reduced secretion of hydrogen ions and more ammonium is excreted
Disorders of the acid- base balance
- Metabolic acidosis: increase in the amount of absolute body acid (DKA, severe diarrhoea)
- Metabolic alkalosis: HCO3 - is increased, usually as the result of excessive loss of metabolic acids (diuretics and vomiting)
Acid base balance
- Excretion of H+ ions
- Reabsorption of HCO3-
RAAS
- The Renin-Angiotensin-Aldosterone System (RAAS) is a hormone system that regulates blood pressure, fluid and electrolyte balance, and systemic vascular resistance
- Angiotensin II will cause MAJOR vasoconstriction
and help increase the blood volume by causing the kidneys to conserve sodium and water and triggers the release of aldosterone and ADH (antidiuretic hormone).
Vitamin D metabolism - Hepatic role
- undergoes two enzymatic hydroxylation reactions.
- The first takes place in the liver,
- The second reaction takes place in the kidney,
- 25OHD, the precursor of calcitriol, is the major circulating form of vitamin D
Vitamin D metabolism - Renal role
- regulated by two hormones, up- regulation via parathyroid hormone (PTH) and down-regulation of FGF23
- Low serum phosphorus levels stimulate calcitriol synthesis, whereas high serum phosphorus levels inhibit it.
- Following its synthesis in the kidney, calcitriol binds to DBP to be transported to target organs.
Plasma phosphate concentration
- Calcitriol: Stimulates Ca2+ and PO43- uptake from GIT, Stimulates renal reabsorption of Ca and PO43-
- PTH: Stimulates rapid transfer of Ca2+ and PO43- from bone and stimulates slower bone resorption, ↑excretion of PO43-, Stimulates reabsorption of Ca2+
- FGF23: Increases renal excretion of PO43-, Increases renal reabsorption of Ca2+
Renal handling of calcium
- 98% of ultrafiltrated calcium is reabsorbed along the nephron, in the proximal tubule and the thick ascending limb (TAL) of the loop of Henle and in the distal convoluted and connecting tubules (DCT-CNT)
- No reabsorption in the collecting duct, so that this segment is dependent on the load of calcium delivered by the connecting tubule and on its ability to defend against precipitation by diluting and acidifying the final urine.
