ANAT2011 - Anatomy/Histology of Core Body Functions

epithelial tissue

covers body surfaces, lines body cavities, and forms glands, functions - protection, secretion, absorption

endothelium lines

blood vessels

connective tissue

contains cells plus ECM - protein fibres (collagen and elastin + ground substance), mostly fibroblast cells that secrete ECM, is a matrix for other structures (vessels, nerves, glands)

ground substance contains

proteoglycans, glycoproteins and polysaccharides that trap water

loose connective tissue

has lots of ground substance

dense connective tissue

less cells, more protein fibres

specialised connective tissues

blood, bone and cartilage

muscle tissue

networks of connected nerve cells (neurons) and their supporting cells (glia), neurons transmit electrical impulses and connect to other neurons via synapses where they release chemical neurotransmitter molecules

peripheral neurons

have specific sensory receptors that receive information from the external and internal environment and relay this information to other neurons and integration occyrs

motor neurons

relay information back out to the body enabling physiological response

neural tissue in GIT

can operate semi-independently to enable movements of the GIT, gastric acid secretion, changes in local blood flow and gut hormone release

visualise tissues using microscopy considers

plane of section, resolution of microscope, quality of staining

GIT walls of tract layers

mucosa, submucosa, muscularis externa and serosa/adventitia

GIT mucosa

mucous membrane, secretes mucous to stop pathogens and prevent dehydration, lines the digestives, respiratory and reproductive systems

GIT mucosa contains

single or stratified epithelium, lamina propria - loose CT underneath epithelium that contains blood vessels and immune cells, muscularis mucosa - circular layer of smooth muscle for localised movement

GIT submucosa

dense irregular CT embedded with glands, lymph nodes, Meissner plexus, larger vessels that send branches to the mucosa, muscularis externa and serosa

GIT muscularis externa

usually 2 or 3 layers of smooth muscle arranged in different orientations, for peristalsis, peripheral nerve plexi between layers - inner circular layer and outer longitudinal layer

GIT serosa/adventitia

simple squamous epithelium (mesothelium), loose or dense CT with adipocytes, nerves, blood vessels or lymphatic vessels, adventitia contains no epithelium and occurs where structure is attached to another structure

histological features of oesophagus mucosa

stratified squamous epithelium, thick muscularis mucosa

histological features of oesphagus submucosa

many mucous glands in upper esophagus for lubrication

histological features in oesphagus muscularis externa

striated muscle in upper 1/3, striated and smooth in middle 1/3, and smooth muscle in lower 1/3

histological features in oesophagus sphincters

form in circular smooth muscle layer, prevents air entry to prevent reflux

rugae

folds of mucosa and submucosa which allow for stretch

stomach mucosa

simple columnar epithelium, gastric glands and pits, lamina propria - loose CT with immune cells, lymphocytes, plasma cells, eosinophils and macrophages, muscularis mucosa very thin

gastric pit

where the surface epithelium dips down into the lamina propri

gastric gland

branched tubular variety of cell types

enteroendocrine cells

hormone secreting gastrin VIP

mucous cells

located between the epithelial cells, most abundant in neck of gland, renewed every 3-5 days, secrete mucous, nucleus at base of cell, apical cytoplasm filled with mucous

parietal cells

secrete HCl and intrinsic factor, large triangular shaped cells, 150-200 days, intracellular canaliculi system that opens into lumen of gland, numerous microvilli projections, mitochondria

chief cells

located deep in the gland, protein secreting (pepsinogen), rough ER

pepsinogen + HCl

pepsin that turns protein → peptides

enteroendocrine cells

G cells, enterochromaffin cells where secretion is regulated by gastric contents released into CT near blood vessels, small cells with short microvilli

stomach submucosa

dense irregular connective tissue, vessels, Meissner nerve plexus, adipose

stomach muscularis externa

3 layers of smooth muscle, vessels, nerves between Auerbach plexus (myenteric plexus)

plicae circulares

mucosal surface circular folds

small intestine mucosa

absorption and secretion, villi covered with simple columnar epithelium, enterocytes, some goblet cells, plicae, villi, microvilli, intestinal glands (crypts) in lamina propria continuous with epithelium at base of villi

small intestine lamina propria

fenestrated wide lumened capillaries, circulating immune cells, small clusters of smooth muscle cells

intestinal gland epithelium

paneth cells secrete peptides for antimicrobial effect to regulate normal flora of SI and enteroendocrine cells to release hormones with endocrine and paracrine function

enteroendocrine cells with endocrine function

CCK and secretin increase pancreatic and gallbladder activity, motilin initiates gastric and intestinal motility

enteroendocrine cells with paracrine function

somatostatin inhibits and histamine stimulates acid secretion

small intestine submucosa

dense irregular CT, large blood vessels and lymphatic vessels, Meissner nerve plexus, Brunner’s glands that produce mucous alkaline secretion, Peyer’s patches

duodenum submucosa

dense irregular CT with Brunner’s glands

ileum

Peyer’s patches

small intestine muscularis externa

inner circular smooth muscle layer for segmental contraction to mix contents and outer longitudinal smooth muscle layer for peristalsis, Auerbach plexus of myenteric nerves located between the smooth muscle layers

large intesine function

absorption of water and electrolytes, addition of mucous for lubrication and elimination of waste

colon mucosa

no villi, numerous simple tubular glands = crypts of Lieberkuhns which extend through full thickness of the mucosa, stem cells in crypts divide to produce all epithelial cells, enterocytes and goblet cells live for only 6 days before shed into lumen

colon epithelium

enterocytes - simple columnar epithelial cells, goblet cells that secrete mucous, enteroendocrine cells, intraepithelial lymphocytes

large intestine colon submucosa and muscularis externa

teniae coli, between these bands the longitudinal layer forms a thin sheet

anal canal upper region

simple columnar epithelium, numerous glands and goblet cells

anal canal lower region

stratified squamous epithelium, numerous glands

anal columns

vertical folds of mucosa and submucosa to allow stretch and contain rectal arteries and veins

enlarged dilated vessels in anus

harmorrhoids

oesphagus

25cm long muscular tube from pharynx to stomach, C6 to T11

oesophagus anterior relationships

trachea down to T4, left main bronchus

oesphagus posterior relationships

vertebrae posterior to the upper 2/3 of the oesophagus, then the aorta passes behind the oesphagus

stomach relationships

anterior - left lobe of liver, posterior - pancreas and left kidney

stomach internal features

rugae (mucous membrane of the stomach forms folds) which flatten as stomach distends, has 3 muscular wall layers

stomach muscular wall layers

inner oblique, middle circular, outer longitudinal

liver surfaces

diaphragmatic and visceral, meet anteriorly at a sharp inferior border

liver external features

falciform ligament demarcates left and right lobes and ligamentum teres the thickening in lower free edge of the falciform ligament

liver blood supply and drainage

hepatic artery brings oxygenated blood to liver, portal vein brings deoxygenated blood to liver, liver is drained by 2-3 hepatic veins to the inferior vena cava

portal triad

common hepatic duct, hepatic artery, portal vein

extrahepatic biliary system

gallbladder, cystic duct, common pancreatic duct, bile duct. bile duct opens into duodenum at major duodenal papilla where it mixes with pancreas secretions

pancreas

located on posterior abdominal wall between duodenum and spleen, curves around vertebral column and ascends to spleen

spleen

functions - filter blood, store rbc, produce lymphocytes and antibodies, remove old rbc, soft with a thin fibroelastic capsule, long axis is oblique and parallel to 10th rib

foregut

from distal esophagus to the entry of the bile duct into the duodenum

midgut

continues 2/3 of the way along the transverse colon

hindgut

from distal 1/3 of transverse colon to anal canal

GIT arterial supply

3 unpaired branches of abdominal aorta - celiac trunk (foregut), superior mesenteric artery (midgut), inferior mesenteric artery (hindgut)

GIT venous drainage

splenic vein (foregut), superior mesenteric vein (midgut), inferior mesenteric vein (hindgut)

duodenum

shortest 25cm, circular folds found in all but the first cm called the duodenal cap

bile duct and main pancreatic duct open at

major duodenal papilla

jejunum and ileum

longest, 4-7m

proximal 2/5

jejunum

distal 3/5

ileum

jejunum absorption rate

greater, food passes more quickly

ileum absorption rate

slower

jejunum characteristics

thicker diameter, longer vasa recta arteries, less fat translucent windows, less fat in mesentery, fewer arterial arcades, thicker walls, circular folds more numerous and closely packed

ileum characteristics

thinner diameter, shorter vasa recta arteries, more arterial arcades, more fat in mesentery, more fat, thinner walls, circular folds are fewer and sparse

ascending colon

illeocaecal valve to right colic flexure

transverse colon

between left and right colic flexures

descending colon

right colic flexure to pelvic brim

sigmoid colon

pelvic brim to S3 vertebral level

colon characteristics on external surface

teniae coli muscles, haustrations, epiploic appendages

caecum

5-7cm long, wide, below level of illeocaecal junction, 3 taeniae coli converge on base of appendix, illeocaecal valve limits reflux into ileum

vermiform appendix

3-15cm

rectum

starts at SV3 at the rectosigmoid junction, transverse rectal folds present, 3 curvatures present

rectum

12cm long

anal canal

2.5-4cm long, external anal sphincter, internal anal sphincter, anal valves

skin functions

thermoregulation, physical barrier, sense organ, immunological, endocrine, exocrine

skin basic structure

epidermis, dermis, hypodermis

skin appendages

hair, hair follicles, sweat glands, sebaceous glands, nails

epidermis

keratinised stratified squamous epithelium, continual differentiationa and desquamation

dermis

connective tissue, tensile strength

hypodermis

adipose tissue

medial malleous epidermal thickness

0.056mm

plantar surface epidermal thickness

0.172mm

dorsum of foot epidermal thickness

0.596mm

epidermis layers

stratum corneum, stratum granulosum, stratum spinosum, stratum basale

stratum basale

single cell layer, rests on basal lamina, stem cells → keratinocytes, small cuboidal, nuclei close together, cells contain melanin