The bs 2

Steps of deep wound healing

1: Hemostasis = Blood floods the wounded site through the punctutered vessels and clots the wound

2: Inflammation at the site occurs

3: Proliferation = Fibroblasts produce granular tissues and an extracellular matrix, this is referred to as scar tissue

4: remodelling = The scar tissue’s EM begins to degrade and the scar fades, being replaced by whatever

Layers of skin from top to bottom

Epidermis:

• Stratum corneum

• Stratum lucidum (only in thick skin)

• Stratum granulosum

• Stratum spinosum

• Stratum basale

Dermis:

• Papilliary dermis

• reticular dermis

Hypodermis

Testical histology

Inside of seminferous tubules

• Spermatogenic cells which become sperm

• Sertoli cells which support and protect spermatogenic cells

In the intersitital space

• Leydig cells which synthesize testosterone

What is diapdesis

White blood cells squeezing through gaps in the squamous epithelium of capilliaries which have increased permeability due to vasodilation

Hormonal control of spermatogenesis - Stimulation

Puberty stimulates the hypothalamus increase GnRH secretion

GnRH stimulates the anterior pituitaries gondatrophic cells to increase LH and FSH secretion

LH stimulates leydig cells to secrete testosterone

Testosterone and FSH stimulate sertoli cells to facilitate spermatogenesis

Hormonal control of spermatogenesis - Inhibition

Testosterone inhibits LH and GnRH secretion

Sertoli cells secrete inhibin which inhibits FSH secretion

Structure of the enteric nervous system:

Location, supplies and structure

The ENS refers to ganglia found within the walls of the intestines

Myenteric plexus

• Location = between longitudinal and circular muscle

• Supplies = smooth muscle layer

• Structure = large ganglia regions

Submucosal plexus

• Location = between circular muscle and muscularis mucosae

• Supplies = mucosal muscularis

• Structure = smaller ganglia

Functions of the enteric nervous system

Regulation of

• Gastrointestinal motility (peristalsis/persitaltic reflex)

• Secretion of fluids

• Nutrient absorption

• Gut-brain axis

Main neurons found in the ENS

Motor neurons in the myentric plexus = control motility of the longitudinal and circular muscle

Motor neurons in the submucosal plexus = controls secretions

Interneurons = connect the neurons of the MP and SMP

Sensory neurons such as stretch receptors and chemoreceptors

Effect of parasympathetic activity in the gut

Increased GI secretion and motility

Effect of sympathetic activity in the gut

Decreased GI secretion and motility

What is the peristaltic reflex

When a stimulus in the gut lumen is detected ascending interneurons are activated which connect to excitatory motor neurons. Causing a contraction orally (above the bolus)

Activation of descending interneurons, which are are connected to inhibitory motor neurons, cause the muscle to relax anally (below the bolus) to propel the contents along.

Small intestine villi:

Location, structure and function

Location:

• Attatched to circular fold

Structure:

• Single lacteal

• Venule and arteriole with capiliaries connecting them

Function:

• Absorbs nutrients into blood (capilliary) or lymph (lacteal)

Mucosa

Mucosa = innermost layer, has 3 parts

• Non-keratinized squamous epithelium for absorption and secretion

• Lamina propia which is CT with vessels and immune cells

• Muscularis mocasa which is a thin layer of folds that create SA

Submucosa

Contains:

• connective tissue which supports the muscosa

• Mucous secreting glands that protects and moistens the lumen

• Blood vessels and lymphatic vessels for absorption

• SMP for regulation

Muscularis externa

Contains:

• Circular layer for constriction which supports mixing

• Longitudinal layer which shorts the tract, supporting propulstion

• MP for regulation

Adventita and serosa

Adventitia = Outermost layer of fixed organs:

• Fibrous connective tissue which helps protect anchor GI tract to surrounding structures

Serosa = Outermost layers of free floating oragans

• Secretes serous fluid for lubrication

• Has a thin connective tissue layer

Small intestine mucosa epithelium cell types

Absorptive cells which digest and absorb from chyme, they have microvilli

Goblet cells that secrete mucus

Cells lining the crevices, forming the instestinal crypt/gland which includes

• the above

• Paneth cells = basically neutrophils

• Enteroendocrine cells = which include

  • S cells - secrete secretin

  • CCK cells - secrete cholecystokinin

  • K cells - secrete glucose-dependent insulinotropic peptide

Cell types in submuscosa and lamina propria of small intestine

Submucosa of duodenum = duodenal glands which secrete mucus to neutralize gastirc acid

lamina propria (mostly ileum) = MALT and peyers patches

Segmentation

Spreads out material in both directions by alternating contraction of circular muscle

Peristalsis

Propels material forward via rhythmic contraction of the longitudinal muscle

Parts of the stomach

Cardia = opening of the stomach

Fundus = rounded superior portion of the stomach

Body = inferior to the stomach

Pyloric part = end of the stomach, 3 parts

• Pyloric antrum = connects body to stomach

• Pyloric canal

• Pylorus = Leads to duodenum

Stomach cell types

Mucus neck cells - secrete mucus

Chief cells - secrete pepsinogen

Parietial cells - secrete HCL and intrinsic factor

G cells - secrete gastrin

Large instestine pathway

Food moves into the caecum

Food moves up the ascending colon

Through the tranverse column

Down the descending column

Through the sigmoid column

Into the rectum

Haustra

Haustra = Bubbles formed by contraction of seperated bands of longitudinal muscle (teniae coli)

• Uncoordinated, food moves randomly

Large intestine functions

Recovery of water and electrolytes

• Sodium is actively absorbed by sodium channels

• Potassium channels diffuse,

• Chloride ions channels are coupled with bicarbonate ions

• High intracellular electrolye presence drives osmosis

Formation and storage of feces

Fermentation of indigestible food

• Bacteria ferment indigestible carbs into short-chain fatty acids and methane gas

Lipid digestion

n the mouth -  lingual lipase

IIn the stomach - lingual + gastric lipase

Bile salts in the duodenum emulsify large fat globules to smaller ones

Pancreatic enzymes breakdown most of the lipids

Lipid absorption

Micelles formed from bile salts surround lipids

They travel to brush border where lipids diffuse out of micelles and into absoprtive cells

Chylomicrons form and exocytose out of the micro and into the nomal villi

The chylomicrons diffuse into the lacteal

Lipid transportation

Chylomicrons travel through the lymphatic system enter blood via the thoracic duct

Lipids are transported through the blood to the liver by proteins

Lipids are cleared in the liver quickly by lipoprotein lipase where they are metabolised

Carbohydrate digestion

In the mouth - salivary amylase hydrolyses starch

In the stomach - some amylase works

In the small intestine - pancreatic amylase, maltase and sucrase hydrolysise amylase and amylopectin further into glucose

In the large intestine indigestibles are fermented

Carbohydrate absorption

Absorptive cells uptake glucose via Na linked transportes 

Glut 2 cells transport glucose into the bloodstream

Protein digestion

In the stomach - HCl denatures proteins and pepsin breaks down long chains into smaller ones

In the small intestine - the pancreatic juices proteases: trypsin, chymotrypsin, carboxypeptidase, and elastase breakdown chains into tri and di peptides

Protein absorption

H+ co transporters transport di and tri peptides into the absorptive cells where they are broken down into amino acids and diffused into the bloodstream

Menopause

Occurs due to the female running out of ovarian follicles. Hence less oestrogen and progesterone is secreted in response to FSH and LH.

Low oestrogen and progesterone lead to copious amounts of FSH, LH and GnRH secretion.

Menstrual phase

Ovarian cycle:

FSH causes follicles to develop

Uterine cycle:

Stratum functionalis sloughs of and exits

Preovulatory phase

Ovarian cycle:

Secondary follicles have formed and release oestrogen. A dominant follicle releases substantially high amounts of oestrogen leading to FSH inhibtion, the decline of which kills the other secondary follicles

The secondary follicle matures into a mature follicle and attatches to the ovarian wall

Uterine cycle:

Oestrogens stimulate the stratum basalis to produce a new stratum functionalis, leading to the endometrium to double in thickness

Ovulation

Ovarian cycle:

Mature follicles high oestrogen secretion stimulates the secretion of GnRH, FSH and LH. The high LH levels cause the mature follicle to rupture and release the secondary oocyte

Postovulatory phase

Ovarian cycle:

The remaining follicular elements collapse and differentiate forming the corpus luteum. This complex releases the ovarian hormones relaxin, inhibin, oestrogen and progesterone, which suppresses LH

If fertilization occured the embryo releases hCG which sustains corpus luteum

If fertilization does not occur the corpus luteum degenerates

Uterine cycle:

Progesterone and oestrogen stimulate the growth of the endometrial glands and blood vessels, which produce an optimal environment for embryo nourishment

If fertilization does not occur the corpus luteum no longer secrets progesterone and oestrogen, triggering menstruation

Sexual intercourse

Pre-ejaculation:

• Male reflex = Erection and lubrication

• Female reflex = Lubrication and engorgment

Ejaculation:

• The semen immediately coagulates, holding it close to the cervix where it slowly decoagulates and releases sperms

• Must occur during the ovulation as outside this time the cervical mucus is too thick and acidic, acting as a barrier

Pathway of fluid through nephron

bowmans capsule → promximal convoluted tubule → descending limb of loop of henle → ascending limb of loop of henle → distal convoluted tubule

Promximal convoluted tubule

Histology = Simple cuboidal epithelium with microvilli

Loop of henle

Histology = simple squamous

Juxtaglomelular apparatus

Produces renin

Distal convoluted tubule

Histology = simple cuboidal

Pertibular capilliaries

A system of capilliaries surrounding the renal tubules, they’re involved in the reabsoprtion of substances

Vasa recta

Blood vessels parallel to the loop of henle

Uses a countercurrent mechanism to support reabsoprtion of nutrients and deposit water into the medulla

Blood flow through the kidney

Renal artery → segmental artery → interlobal artery → arcuate aratery → interlobular artery → afferent arteriole → glomerulus → efferent arteriole → pertibular capilliaries → vasa recta → renal vein

Glomeruluar filtration

Involves components of blood being pushed through the glomerular filtration membarne (capilliary endothelium + basement membrane + podocytes) into the bowmans space

Seperates water, electrolytes, glucose, amino acid and waste

Proximal convoluted tubules role in urine formation

Reabsorption:

• The majority of reabsorption occurs in the PCT

Secretion:

• Secretes some urea, K+ and H+

Distal convoluted tubules role in urine formation

The DCT is involved in fine-tuning electrolye concentration

Principle cells: 

• Reabsorb sodium

• Secrete potassium

Intercalated cells

• Reabsorb potassium and bicarbonate

• Secrete H+

Loop of henle’s role in reabsorption

Regulates fluid volume and osmolarity seperately to establish an osmotic gradient

Descending limb = passive reabsorption of water due to high solute concentration in the medulla

Ascending limb = impermeable to water but actively transports solutes out

Purposes of glucose, amino acid, ion and water reabsorption

Purpose of potassium and hydrogen ion secretion

To maintain acid base balance

ADH influence

Decreases urine production by:

• Making DCT and collecting duct principal cells more permeable

• Inserts aquaporins into these cells

Prodcution is regulated by hydration levels

Renin-angiotensin-aldosterone system pathway

Renin (kidney) + angiotensinogen (liver) → angiotensin I + angiotesin-converting-enzyme → angiotensin II

Renin production

Secreted from juxtaglomerular cells after the macula densa senses low fluid flow or low sodium concentration

Angiotensin II functions

Constriction of afferent arterioles which increase BP

Reduction of GFR which conserves water and salt

Triggers the release of aldosterone

Aldosterone

Released from the adrenal glands:

• Inserts sodium channals and sodium/potassium pumps into DCT and collecting duct cells

Results in more sodium and water reabsorption and more potassium secretion

Kidney production of EPO and Vitamin D

EPO = more blood = more oxygen

Vitamin D = calcitriol

Micturition reflex

Sensory stretch receptors in the bladder wall detect urine filling, triggering signals to the brain.

The brain responds by relaxing the involuntary internal urethral sphincter at the bladder-urethra junction.

Simultaneously, voluntary control allows the brain to signal the relaxation of the external urethral sphincter at the external opening of the urethra.

This coordinated action enables conscious control over urine flow during urination, ensuring proper bladder emptying while maintaining continence.