Unit 4 Flashcards
What does the digestive system do? (4)
- ingests nutrients
- digests nutrients
- absorbs nutrients
- eliminates waste
Problems with the digestive system?
- avoid digesting self (acid reflux)
- one entrance, one exit
- compartmentalize
What is digestion?
a combination of cell/enzymatic and organismal multistep process of consuming nutrients, breaking them apart, absorbing them, and eliminating the waste materials
Ideal Absorptive Digestive Structures
- high SA (folds, villi, loops)
- thin and long (more SA, more absorption)
- high mitotic rate and mucous levels (resist abrasions)
- buffer regulation (pH)
- elastic and smooth muscle (move materials)
- highly vascular
Why is the digestive process multi-step and occur in different compartments?
To protect the body from digesting itself
The GI tract is…
composed of single unite smooth muscle and moves at one pace
Two Types of Contraction
- Tonic
- Phasic
Tonic Contraction
long, slow, steady contraction (minutes or hours)
- occurs at fundus or sphincters
Phasic Contraction
short, fast, adapting (seconds)
- occurs in small intestine, antrum
Motility and Contractile Patterns (3)
- Migrating motor complex
- Peristaltic Contractions
- Segmental Contractions
Migrating Motor Complex
- occurs when tract is empty
- travels stomach to large intestine
- passes slowly (~90 mins)
- “housekeeping” - gets last of food left in the system
- tonic and deliberate
Peristaltic Contractions
- occurs following a meal
- move bolus through GI tract
- relatively fast
Segmental Contractions
- occur in intestine
- are paired contraction/relaxation events
- mix chyme - yield no net movement
- chyme = combo of partially digested food, saliva, etc.
Digestive Muscle vs Skeletal/Cardiac Muscle
Digestive muscle has
- multiple layers
- cannot be strengthened by “working out”
- different timing
Digestive Smooth Muscle
- in visceral organs (gut)
- generate force for gross movement
- consumes little oxygen (allows for prolonged contraction
Classes of smooth muscle
- are based on physical structure/organization (existence of interconnections and location of autonomic varicosities)
- Include SINGLE UNIT and MULTI-UNIT
Single Unit Smooth Muscle
- fibers contract simultaneously (connected by gap junction, share action potentials)
- exhibit complete contraction (all fibers participate in contractions)
- found in walls of viscera (blood vessels, intestinal tract)
- stimulate only a couple cells to stimulate the wave motion
Multi Unit Smooth Muscle
- allow for very fine levels of movement
- fibers are separate cells and must be stimulated separately
- varicosities embedded throughout the muscle (allows for fine control of contraction)
- class is found in iris, ciliary bodies, uterus
Organization of Contractile Filaments
- arranged in bundles
- extend diagonally across cell
- form lattice around nucleus
- yields globular form upon contraction
Filament Arrangement
- Actin attaches to dense protein bodies and terminates at protein plaques in membrane
- Myosin lies between actin filaments and is “covered” with heads”
- power stroke is essentially the same
Compartmentalizing …
- provides protection from digesting self
- allows high efficiency
- “assembly line”
- high extraction ability
Digestive Roles of the Oral Cavity (3)
- securing food (not really for humans) - jaws, teeth, tongue
- ingesting food - teeth, jaws. tongue, mouth
- digesting food - teeth, jaws, glands (salivary)
The Buccal Cavity (=oral)
the entrance to digestive system defined by lips, palatoglossal arch
- can also include nasal
Lips
- outer margin of the oral opening
- all vertebrates have them
- follow tooth line, meet at angle of the jaw
- typically pliable, can be fleshy
Cheeks
- are formed by lips meeting well forward of angle of jaw
Why have cheeks?
- storage of food
- help with creating pressure for nursing as a baby and pressure gradient
Teeth (The Buccal Cavity)
- aid in catching and holding prey
- aid in mechanical and chemical digestion ***
- arose from bony armor from primitive fishes
- are vertebrate synapomorphy
Bony Teeth
- have cellular and acellular components
- are coated in mineralized deposits for strength durability
- made for life
- deeply rooted in jaw
INTEGUMENTARY
Types of Teeth
- Incisors (4/4)
- Canines/Cuspids (2/2)
- Premolars/Bicuspids (4/4)
- Molars (6/6)
Incisors
sharp, front teeth you use for biting into food
Canines/Cuspids
have a pointed edge (cusp) to tear up food, are superb for piercing tough or fleshy foods
Premolars/Bicuspids
have an overall flatter shape with two rounded cusps useful for mashing foods
Molars
posterior and largest teeth, have several pointed cusps to crush food so its ready for swallowing
Carnacial Pair
not “sharp” but align to shear
The Alimentary Canal
- the primary region of digestion
- has 4 generalized regions
- has distinctive, variable structure/composition
- high vasculature
~~high immune presence
~~ lots of veins, arteries, lymphatic vasculature
Mucosal Layer of Alimentary Canal
- thin
- thin layer of muscle
Submucosa of Alimentary Canal
- interic (digestive) nervous system
- more vasculature
- nerves
Muscularis of Alimentary Canal
- lots of muscle
- nerves
- peristaltic and segmental contractions
Serosal Membrane of Alimentary Canal
Protective layer
Why does your belly rumble?
- feed forward signaling
- muscles turn in anticipation and preparation for food coming in (almost signifying that the stomach is empty and is preparing the system to digest more)
The Esophagus
- extends from pharynx to stomach
- conducts food bolus to stomach
- has mucus lining, can be cornified (not humans)
- has longitudinal folds
- is “collapsed” pre/post ingestion (help food pass the large lungs and heart to get food to the stomach
Deglutition ~ oral phase
- voluntary
- begins with tongue pushing the bolus to the back of the oral cavity and into the oropharynx
Deglutition ~ pharyngeal phase
- involuntary
- stimulation of receptors in the oropharynx sends impulses to brain stem
- pharyngeal constrictor muscles moves the bolus through the oropharynx and laryngopharynx
- UES relaxes and food enters esophagus
- tongue pushes back and starts pushing food down (irreversible)
Deglutition ~ esophageal phase
- peristalsis propels bolus through the esophagus and toward the stomach
The Stomach
- primarily used for food storage
- also engages in mechanical and chemical digestion
- churns bolus
- releases “gastric juice”
What is the stomach?
- a J-shaped extension of the alimentary canal
- is bounded by cardiac, pyloric sphincters
- is divided into 3 main regions
3 Regions of the Stomach
- cardiac
- fundus
- pylorus
Cardiac Region of the Stomach
- transitional area between esophagus and stomach
- has glands with mostly mucus secreting cells
- houses cardiac sphincter
Fundus Region of the Stomach
- the largest region of the stomach
- highly muscular
- has parietal cells - release HCl
- has chief cells - release proteolytic enzymes
Pylorus Region of the Stomach
- narrow region before small intestine
- is lined with mucus secreting cells
- houses pyloric sphincter
- pH buffer
Intestines
- primary site for chemical digestion and absorption
- is divided into small and large intestines
- has distinctive, variable substructure/composition
- digests and absorbs more than any other part of the system
- changes based on age, conditions
Small Intestine
~ 18-20 ft long
- the main alimentary region of chemical digestion and nutrient absorption
- has 3 distinct regions
3 Regions of Small Intestine
- Duodenum
- Jejunum
- Ileum
Duodenum
- follows pyloric sphincter posteriorly
- received secretions from pancreas, gall bladder
- 1st portion, very busy
- ensure pH is on point for enzymes from pancreas and gall bladder
Jejunum
- mostly nutrient absorption
- uses facilitated diffusion/diffusion to move and absorb nutrients and materials
- vary between organisms
Ileum
- mostly mineral absorption
- uses facilitated diffusion/diffusion to move and absorb nutrients and materials
- vary between organisms
Segmental Contractions…
mix the bolus because the goal is homogeneity
Large Intestine
- is separated from small intestine by ileocolic valve – sphincter muscle
- lacks villi
- reduced SA
Function of Large intestine
- absorbs water
- concentrates feces
- reuptakes water which makes feces more solid
Kidney Function
- regulation of extracellular fluid volume
- maintenance of ion balance (Na, Ca, K)
- homeostatic regulation of pH
(if low pH, remove H+)
(if high pH, retain H+) - excretion of wastes/foreign substances
(metabolic wastes and creatine) (foreign substances - saccharin and benzoate)
Kidney must have…
- high SA
- high vasculature
- a way out
Kidneys (parts)
- cortex
- medulla
- renal pelvis
Kidney Microanatomy (10)
- nephrons
- afferent arterioles
- glomerulus
- efferent arteriole
- Bowman’s Capsule
- proximal tubule
- loop of henle
- distal tubule
- collecting duct
- peritubular capillaries
Nephrons
- are functional units of kidneys (10^6 per kidney)
- composed of vascular and tubular elements
Afferent Arterioles
from renal artery to nephron
Glomerulus
- is a ball like capillary network
- is found in kidney cortex!!!!! (if in medulla you would be “fucked” bc of reversal)
- is site of filtration (out of blood into nephron)
Efferent Arteriole
- blood from glomerulus
Renal Portal System
Afferent Arteriole -> Glomerulus -> Efferent Arteriole
Bowman’s Capsule
- surrounds glomerulus
- receives filtrate
- is part of renal corpuscle (=capsule + glomerulus)
Proximal Tubule
- extends from capsule
- conducts filtrate
Loop of Henle
- is a hairpin loop
- is composed of limbs
~ descending and ascending - functions for water retention (get the most water back as possible)
Distal Tubule
- contains flow from loop
Collecting Duct
- takes input from many nephrons
- passes through cortex, medulla
- drains into renal pelvis
Peritubular Capillaries
- branch off efferent arterioles
- surround loop of henle, tubules
- help in reabsorption
Overview of Kidney Function
- Filtration (take stuff out, movement of fluid from blood to nephron)
- Reabsorption (materials needed, filtered material reenters blood)
- Secretion (get rid of stuff not needed, moves selected molecules into nephritic fluid)
Volume and Osmolarity in the Nephron
- urinary filtrate
- proximal tubule
- loop of henle
- distal tubule/collecting duct
- Final urine
Urinary Filtrate
- enters nephron through Bowman’s Capsule
- averages 180L per day (fluid is filtered several times)
- is nearly osmotic with blood (nearly isotonic at 300mOsM)
Proximal Tubule (Volume and Osmolarity)
- reabsorbs isosmotic fluid (190L-> 54L – 70% reabsorption)
- transports solutes out of lumen
- “transports” fluid by osmosis
Loop of Henle (Volume and Osmolarity)
- dilutes filtrate in lumen without adding fluid
- solute reabsorbed > water reabsorbed – reabsorb solute without losing water
- decreases both volume and osmolarity
54L -> 18L
300 mOsM -> 100mOsM
Distal Tubule/Collecting Duct (Volume and Osmolarity)
- regulates salt and water balance
- use reabsorption and secretion (typically meal ions and bad stuff)
Final Urine
- averages 1.5L/day
- ranges 50-1200mOsM
- condition dependent
Why filter 180L/day? Isn’t the goal efficiency?
- depends on what the body needs and provides the body with real time monitoring
- monitor changes in cell volume
- water is the thing we need most so this allows us to filter and retain as much as possible
How might the process of filtration occur?
- PRESSURE GRADIENT AND FILTRATION
- hydraulic pressure
- osmotic pressure
Hydraulic Pressure
- pressure in capillaries > pressure in capsule that leads to filtration
- pressure from water movement
Osmotic Pressure
- pressure from movement of ions
- pressure in capillaries > pressure in capsule leads to reabsorption
Hydrostatic Pressure
- pushing of fluid onto the chamber (surface)
- Capillary pressure < capsule pressure -> Reabsorption
Movement for Filtration
Glomerulus->Bowman’s Capsule - release isosmotic fluid
Proximal Tubule - isosmotic fluid travels to LoH
Descending Loop of Henle - water exits and flows with gradient
Ascending Loop of Henle - ions pumped out without H2O movement
Distal Tubule - hyposmotic fluid enters
Collecting Duct - permeability of water determines [urine]
Prep Urine for Secretion
Process of Filtration
- Glomerulus to Bowman’s Capsule - Proximal Tubule
- Surrounded by blood vessel, fluid flows to areas of high concentration to induce reabsorption
- water exits - yields hyper-osmotic fluid
- ion movement (remove), block water movement, dec concentration without changing volume
- Prep Urine
- Permeability of H2O and reabsorb water
What does alcohol do?
- inhibits the H2O absorption
- inc excretion and dehydrates because so much water is expelled to dilute the wastes
