Key Concepts for Test 1 Flashcards
Lacunar stage days 8-12
Primitive syncytium invades the uterine decidua forming gaps in the maternal tissue or lacunae .The trophoblast protrusion are called trabeculae. The lacunae tap the maternal blood vessels
Tertiary Villi (18 - 20 days)
Capillaries form in the villi. All villi are tertiary. The vessel connect to the umbilical vessels carrying blood to the fetus
Villi regression forming smooth chorion
The placenta forms a sphere surrounding the embryo but as gestation progresses:
Villi disappear to the sides and luminal aspect regress to form the smooth chorion (membrane that a baby lives in)
Only villi basal to the implantation site remain as the placenta
Anchoring villi processes
A few villi cytotrophoblasts break through the syncytiotrophoblast.
The cytotrophoblast spread laterally around the implantation site forming a cytotrophoblast shell
The trophoblast shell remains in contact with the maternal tissue throughout gestation
Columns of cytotrophoblast continue to stream out of these anchoring villi to invade the decidua and spiral arteries during the first and second trimesters
Trophoblasts transforming the spiral arteries
Extravillous trophoblasts break through the syncytiotrophoblast layer of the placental villous and invade the spiral arteries
The spiral arteries transform to wide-bore tubes with no muscular wall, lined by trophoblasts and can’t respond to stimuli
Endocrine control of lactation
Prolactin is produced in large amounts in pregnancy and falls at birth.
Suckling of infant induces secretion of prolaction by the anterior pituitary.
Prolactin is stimulated by a neuroendocrine reflex, cutting the nerves to the nipple prevents this reflex
Milk ejection response
Suckling stimulates synthesis and secretion of oxytocin by the posterior pituitary.
Oxytocin induces the contraction of myoepithelial cells of alveoli causing ejection of milk.
Stimulation of female reproductive tract can induce oxytocin release.
Stimuli such as crying and smell of baby can induce MER
Heart Development - before 3 weeks
Heart forms a straight tube on ventral midline. Relies on oxygenation and nutrient delivery via diffusion.
Heart Development - 3 weeks
Heart tube lengthens and starts to form S shaped tube. Primitive atrium moves dorsally towards head and primitive ventricle swings ventrally and towards the tail = cardiac looping
Heart Development - 3.5 weeks
As atrium moves towards head, it passes behind the bulbus cordis. The sinus venosus is carried with the atrium and disappears from our view. as it moves to the dorsal side of the heart, behind the ventricle
Growth is quicker in regions compared to junction, therefore bulging is pronounced. Sinus venosus is hidden and has horn projects on each side attached to three veins
Heart Development - 4 weeks
Cardiac looping has finished
Horns of the sinus venosus now enter the atria on cranial and dorsal side. Interatrial septum forms, beginning chamber formation, one on each side of the bulbus cordis. Primitive ventricle forms caudal apex of the heart. Interventricular septum begins to form at old bulboventricular junction, separating LV and RV
Heart Development - 5 weeks
Sinus venosus is no longer recognisable
Blood returning from body drains mostly to the right side.
Right horn enlarges & contributes to the right atrial wall
Left horn diminishes and eventually forms the coronary sinus (draining blood from cardiac veins back to RA.)
Distal part of Bulbus Cordis splits into Conus cordis and Truncus arteriosus
Heart Development - 6 weeks
SVC & IVC are established
Ridges run lengthwise inside the truncus arteriosus and conus cordis. Ridges run in a spiral and when fusion occurs will form a spiral partition or septum
Heart Development - 7-8 weeks
Aorta (Ao) and Pulmonary trunk (Pt) become separate vessels twisting around another. Caudal part of spiral septum contributes to interventricular septum that separates the two ventricles
Heart Development - Full term fetus
Pulmonary trunks gives rise to left, right pulmonary arteries and ductus arteriosus. Interatrial septum is incomplete allowing blood to pass from RA to LA
Formation of interatrial septum
- Downgrowth of septum primum and formation of L and R endocardial cushion.
- Fusion of inferior and superior endocardial cushion forms septum intermedium (divides atrio-ventricle canal)
- Cell death creates ostium secundum
- Downgrowth of thick septum secundum. Ostium primum completed sealed
- Septum secundum stops growing and foramen ovale forms allowing blood flow for RH to LH
Changes at birth
Resistance decreases
Infant takes first breath, lungs inflate and replaces fluid. Capillaries expand and resistance to blood flow decreases
Blood leaving right ventricle travels through low resistance lung pathway rather than high resistance ductus arteriosus into the systemic circuit.
Blood travels through the left side for the first time
Umbilical vein constricts and is clamped. Venous return to placenta is 0. Inflow to RA from systemic circuit decreases, RA pressure falls
LA pressure exceeds RA pressure. Septum primum closes, the foramen closes separating the two atria
Stages of Lung development - 26 days to 7 week
(embryonic)
Lung bud arises as ventral outpouching and undergoes 3 round of branching, producing the primordia of the two lungs, lung lobes and bronchopulmonary segments
Stages of Lung development - 5 to 17 week
(pseudoglandular)
Respiratory tree undergoes more generations of branching, resulting in formation of bronchi, bronchioles and terminal bronchioles. Lung resembles a gland
Stages of Lung development 16-25
(cancalicular)
Each terminal bronchiole gives rise to 2 or more resp bronchioles. Each divides into 3-6 alveolar ducts lined by cuboidal cells.
Stages of Lung development - 24 week to after birth
(saccular)
Alveolar ducts give rise to thin walled terminal air sacs. Type I alveolar cells are intimately associated with blood and lymph capillaries. Type II alveolar cells develop and begin to produce surfactant.
Stages of Lung development - Late foetal to 8 years
(alveolar)
Number of terminal sacs increases. Alveoli mature through continued thinning of squamous epithelial lining and more intimate contact with surrounding capillaries
Lymph nodes
Dense areas of lymphocytes and macrophages.
Role: Homeostasis of immune, fluid pressure and nutrient transport
Have defined structure with capsule of connective tissue and areas of lymph nodule tissue and sinus tissue
Gut-brain axis
Bidirectional communication between gut and brain
Involves neural, hormonal, and immunological pathways
Neural: Enteric nervous system communicates via vagus nerve
Hormonal: Gut hormones like serotonin, dopamine influence mood, appetite
Immunological: Gut immune cells produce cytokines affecting brain function
Vagal innervation via ENS
Stimulates parietal cells (secrete acid / HCl)
ECL cells (Histamine - stimulates parietal cells
G cells in antrum - (Gastrin - stimulates ECL cells
Inhibits: D-cells in the corpus & antrum (SST)
All acting to enhance HCl secretion for digestion in stomach - chyme
pH < 2 stimulates D-cells in atrum
Stimulation of D-cells - inhibit parietal & ECL cells
Chyme enters the duodenum (lowers pH. Stimulates S-cells (Secretin - stimulate D cells & stimulates pancreas to release bicarbonate)
Both working to counteract release of HCl and bring pH up for enzymes to work
Renal corpuscle formation
Blind ended tube attracted to blood vessel (insinuation) forming capillary tuft (Glomerulus / Glomerular capillaries) then into a renal corpuscle (Bowman’s capsule + glomerulus)
Order of blood supply of multilobar kidney
Aorta
Renal artery
Segmental artery
Interlobar
Arcuate artery
Interlobular artery
Afferent arteriole
Glomerulus
Efferent Arteriole
Blood supply to outer cortex
Capillaries of cortex
Stellate vein
Interlobular vein
Arcuate vein
Interlobar vein
Renal vein
Inferior Vena Cava
Transitional epithelium
Surrounded by a smooth muscle layer and fibro-elastic connective tissue
Urine proofed - with tight junctions between cells and a specialised cell membrane on luminal side
