digestive anatomy intro Flashcards
4 main functions of digestive tract
- digestion; food broken down or converted into form where it can be absorbed
- absorption; released nutrients are taken up by mucosal cells after food is digested
- motility; the GI tract transports food as well as digestive secretions
- elimination of waste; anything that hasn’t been absorbed is expelled from the body
break down of food into small enough parts requires
enzymes, secreted in mouth, stomach, pancreas and small intestine
buccal cavity
aka oral cavity, teeth, tongue and pharynx
oesophagus in birds is
enlarged into crop
small intestine consists of
duodenum, jejunum and ileum
large intestine consists of
colon, caecum and rectum
extrinsic glands/ organs consist of
salivary glands, pancreas, liver
fore-gut fermenters
fermentation takes place BEFORE reaching glandular stomach and small intestine
(ruminants)
hind gut fermesters
fermentation takes place in large intestine and caecum (AFTER food passed through stomach and SI)
cardiovascular system and interaction with digestive system
Blood supplies digestive organs with O2 and energy (processed nutrients)
endocrine system and interaction with digestive system
hormones help regulate digestive gland and accessory organ secretion
integumentary system and interaction with digestive system
helps protect digestive organs
lymphatic system and interaction with digestive system
mucosa- associated lymphoid tissue defends against entry of pathogens; lacteals absorb lipid; lymphatic vessels transport lipids to circulation
muscular system and interaction with digestive system
skeletal muscles provide support, protect abdominal organs and aid in defecation
nervous system and interaction with digestive system
Sensory and Motor Neurons
Intrinsic (enteric nervous system) and extrinsic (autonomic nervous
system – sympathetic and parasympathetic)
Regulate secretions and muscle contraction in the digestive tract
respiratory system and interaction with digestive system
Provide oxygen and remove carbon dioxide
skeletal system and interaction with digestive system
Protect and support digestive organs
urinary system and interaction with digestive system
Aid calcium absorption in the small intestine (via vitamin D activation)
homeostasis
maintenance of relatively constant internal environments
homeostasis requires
- Consistent monitoring: Feedback, usually negative, sometimes positive or pre-emptive
- Capacity to make changes and adjust internal environment: integrated endocrine and neural response
- Defence against external environment; Microbes, Temperature, Water
paracrine response
refers to a hormone which only has effect in
close proximity of the gland secreting it; the signalling cell is close
to the target cell.
endocrine response
hormonal secretion; secreting endocrine cell into blood and to distant target cell via receptors
other functions of digestive system not including nutritional functions
excretion, fluid and electrolyte balance, immunity
to maintain healthy gut:
why
presence of food is essential; enterocytes rely of food to maintain tight junctions between cells
without food in the system:
the permeability
increases and undigested food particles, bacteria and toxins can cross over into the
bloodstream, which can result in sepsis.
MECHANICAL processes of digestion
Prehension
Mastication
Deglutition
Rumination
Storage
Motility of the wall
Defecation
Vomiting
CHEMICAL processes of digestion
enzymatic or non-enzymatic
CHEMICAL processes of digestion:
stomach releases pepsinogen (an enzyme precursor) and acid (non enzymatic secretion) into the lumen, what happens?
The acid activates pepsinogen to form
pepsin which is an enzyme that breaks peptide bonds ‐ protein digestion. The
acid also causes the proteins to unravel and lose their 3‐D structure, aiding in the
breakdown of those bonds by pepsin
SECRETORY processes of digestion
- includes external glands: salivary glands, liver or pancreas
- and internal glands: secretory cells which reside in walls of stomach and intestine
microbiome
community of organisms living together in a specific habitat
microbiota
all living members forming microbiome:
bacteria, protozoa, archaea, fungi, algae
mono =gastric
one stomach ie simple stomach
ruminants
to chew over again; rumen, 4 stomachs
pseudo-ruminants; camelids, 3 stomachs
hind gut fermenters
can survive from lower quality forage
seen in monogastric herbivores
giant panda is a member of the carnivores but is
entirely vegetarian
so the true taxonomic relationships of herbivore, omnivore, carnivore doesn’t necessarily mean diet
carnivores have
meat eating teeth, simple stomach, short intestine
if animal also consumes non-animal food, they are omnivores
omnivores
variety of food
intermediate length digestive tract, medium length intestines
herbivores
- long intestines
- teeth for mechanical grinding
- cellulose in plant cell walls cannot be digested by mammalian enzymes
- micro-organisms needed
- fermentation chamber
coprophagy
eating own feces; increase the effectiveness of digestion
frugivores
animal eats mostly raw fruits or roots, shoots, nuts and seeds
insectivores
eat insects, worms and other invertebrates
sanguinivores
consume blood
4 major tissue types
epithelial, connective, muscle and nervous
epithelial tissue
covers surface of body, and lines body cavities and hollow organs, specialized according to function
connective tissue
supports and binds other tissues together, also includes blood and bone marrow
connective tissue consists of 3 main components
- fibers (elastin or collagen fiber, ground substance and cells)
- connective tissue cell nuclei
- collagen fibers
3 types of muscle tissue
- smooth muscle (around organs; involuntary contraction)
- skeletal muscle (involved in locomotion and posture)
- cardiac muscle (heart)
nervous tissue
regulates and controls the function and activity of the body using both electrical and chemical messengers to
conduct signals from one part of the body to another
4 tunics of tube of the esophagus to the rectum from inner to outer
- tunica mucosa
- tunica submucosa
- tunica muscularis (aka muscularis externa)
- tunica serosa
3 layers of tunica mucosa (inner most layer) from inner to outer
- epithelium; stratified squamous or simple columnar
- lamina propria; connective tissue
- muscularis mucosa; smooth muscle
epithelium is derived from
embryonic endoderm
what layer gives rise to the glands
epithelial layer
Stratified squamous epithelium
provides protection from abrasion; seen in skin and in non-absorbable areas of GIT ex esophagus
Columnar epithelium
elongated cells have lots of cytoplasm, helps them undergo cellular processes, helps in digestion and absorption, often excretory or absorptive or both ex in stomach and intestines
Enterocytes;
absorptive cells of intestine, are simple columnar epithelial cells, line inner surface of small and large intestine, have microvilli to increase SA for absorption
Enterocytes also
secrete hormones such as leptin.
glycocalyx;
surface coat sitting on apical membrane containing digestive enzymes
Base of cell
basolateral membrane
Lamina propria
- Layer of loose connective tissue
- Contains immune cells, small blood vessels (capillaries) and lymphatic vessels (lacteals)
- Carry absorbed nutrients away from GIT and into the circulation
Muscularis mucosae (last layer of Tunica mucosa)
- Layer of small muscle
- Separates the connective tissue layers of the lamina propria and submucosa
Tunica submucosa (second tunic)
- Connective tissue
- Lies directly beneath mucosa
- Contains blood and lymph vessels
- Also contains nerves; submucosal/ meissner’s plexus
- May or may not contain glands
- Important for surgery; strength layer because contains larger bundles of collagen fibers
- Want to make sure we suture into submucosal layer
Tunica muscularis (aka muscularis externa)
- Made up of 2 layers of muscle
- Inner circular muscle; contracting down to mix and propel food
- Outer longitudinal muscle; propels wave along as contraction is going
- Auerbach’s nerve plexus (myenteric plexus)
- Sometimes there is an additional muscle layer
submucosal plexus aka meissner’s plexus
- found in tunica submucosa
- This is a
critical part of the digestive tract’s nervous system. It provides nervous control to
the mucosa
Auerbach’s nerve plexus aka myenteric plexus
- found in tunica musculari
- this is one of two principle components of the enteric nervous system.
Tunica serosa/ adventitia
Tunica serosa
- Connective tissue covered by mesothelium tissue in abdomen
- Fluid so nothing sticks
Tunica adventitia (no mesothelium layer, don’t need fluid, don’t need the slip)
- Connective tissue that blends with surround connective tissue form other organs
- Neck, thorax and anal region
Regulation of the GI tract
Intrinsic innervation (enteric nervous system ENS)
- Submucosal and myenteric (aurbach’s) plexuses
- Local regulation of GI tract
- Paracrine secretion; molecules acting locally
- Hormonal secretion; secreted by the mucosa
Regulation of the GI tract
Extrinsic innervation
- Parasympathetic nervous system (rest and digest) stimulate motility and GI secretions
- Sympathetic nervous system (fight or flight) reduce peristalsis and secretory activity
