Placenta and Fetal Development: A Comprehensive Guide
Placenta Formation
The placenta is a vital organ that develops during pregnancy to facilitate the exchange of nutrients, oxygen, and waste products between the mother and the developing fetus. The journey begins even before implantation.
The fertilized egg, called a blastocyst, contains an outer layer of cells called trophoblasts. These are the key players in placenta formation.
Early Development (Week 1-3)
Implantation: Around 7-10 days after fertilization, the blastocyst implants in the uterine lining.
Trophoblast Differentiation: Within the first week, the trophoblasts differentiate into two layers:
- Cytotrophoblast: This inner layer is a single layer of cells that continues to divide.
- Syncytiotrophoblast: This outer layer is a multinucleated layer formed by the fusion of cytotrophoblasts. It has an invasive role and helps establish connections with the maternal blood supply.
Growth and Invasion (Week 4-8)
Villi Formation: Finger-like projections called villi sprout from the cytotrophoblast layer. These villi will be the sites of exchange between maternal and fetal blood.
Uterine Remodeling: The syncytiotrophoblast secretes enzymes that erode maternal uterine spirals arteries, allowing increased blood flow towards the developing placenta.
Establishment of Exchange (Week 8 onwards)
Lacunae Formation: Spaces filled with maternal blood, called lacunae, appear within the villi.
Fetal Blood Vessel Growth: Blood vessels grow from the embryo into the core of each villus.
The Final Structure
By the end of the first trimester (week 12-14), the placenta is largely formed. It resembles a flat, disc-shaped organ with a rough maternal surface and a smooth fetal surface.
The placenta continues to grow throughout pregnancy, reaching its full size by the third trimester.
Maternal and Fetal Blood Don’t Mix
Although the placenta facilitates exchange, maternal and fetal blood never directly mix. Nutrients, oxygen, and waste products are transferred across a thin membrane separating the two bloodstreams. This ensures a safe and controlled exchange for both mother and baby.
The Placenta’s Role
The placenta is a multi-tasking wonder. Here are some of its key functions:
- Nutrient and Gas Exchange: It allows oxygen, nutrients, and hormones to pass from mother to baby, while removing waste products from the baby.
- Hormone Production: The placenta produces hormones essential for pregnancy maintenance, such as progesterone, estrogen, and human chorionic gonadotropin (hCG).
- Protection: It acts as a barrier against harmful substances and pathogens.
- Immune Support: It plays a role in the developing baby’s immune system.
After Birth
Following childbirth, the placenta detaches from the uterine wall and is delivered as the afterbirth. This marks the end of its crucial role in supporting the developing baby.
Applied Anatomy
Placenta previa: It is the implantation of the placenta over the cervical os, which usually presents as painless vaginal bleeding.
Placenta accreta: The placenta attaches itself too deeply and too firmly into the uterus.
Placenta percreta: The placenta attaches itself and grows through the uterus, sometimes extending to nearby organs, such as the bladder.
Anterior Pituitary (Adenohypophysis)
The anterior pituitary is a small, pea-sized gland located at the base of the brain. It is responsible for producing and releasing a variety of hormones that regulate various bodily functions.
The anterior pituitary is divided into three regions:
- Pars Anterior: This region produces growth hormone (somatotropin), thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicular stimulating hormone (FSH), luteinizing hormone (LH), and prolactin.
- Pars Tuberalis: This region produces dopamine, which inhibits prolactin secretion.
- Pars Intermedia: This region produces melanocyte-stimulating hormone (MSH), which regulates skin pigmentation.
Posterior Pituitary (Neurohypophysis)
The posterior pituitary is a small, pea-sized gland located at the base of the brain. It is responsible for storing and releasing two hormones: oxytocin and antidiuretic hormone (ADH).
The posterior pituitary is divided into two regions:
- Pars Posterior: This region stores and releases oxytocin and ADH.
- Infundibular Stem: This region connects the posterior pituitary to the hypothalamus.
Thyroid Gland
at the lower border of isthmus. Two surfaces of the isthmus: Anterior surface is covered by- The skin ,Superficial and deep fascia. Sternothyroid and sternohyoid muscles. Posterior surface is related to 2nd to 4 deg tracheal rings.
superior thyroid artery (from the external carotid artery)
inferior thyroid artery (from the thyrocervical trunk) :Thyroid nodules Goiter
suprarenal gland 1cm thickness, 3cm width, 5cm length and weight is about 5gm.
Rt suprarenal gland: pyramidal shape and it has apex, base, 3 surfaces and 3 borders.
Apex is related to bare area of liver. Base is related to upper pole of the right kidney.Three surfaces of right suprarenal gland Anteromedial surface is related to the inferior vena cava. Anterolateral surface is related to the right lobe of the liver. Posterior surface is related to the right crus of diaphragm. Three borders of right suprarenal gland
Anterior border: The hilum is present on this border through which the right suprarenal veins drains into the inferior vena cava. Medial border is related to the right coeliac ganglion and right inferior phrenic artery.
Lateral border is related to the liver. Left suprarenal gland: It is semilunar in shape and it has upper and lower end, 2 surfaces and 2 borders. Two ends of left suprarenal gland: Upper end is related to posterior end of spleen. Lower end – The hilum is present near the lower end Two surfaces of left suprarenal gland Anterior surface is related to the- Stomach Pancreas The splenic artery; Posterior surface is related to the left crus of the diaphragm. Two borders of left suprarenal gland: Medial border is convex and is related to-
Left coeliac ganglion Left inferior phrenic artery and Left gastric artery.
Outer cortex part: It is yellowish in color and can be divided into 3 regions Zona glomerulosa: It produce the mineralcorticoids such as aldosterone hormone. It help to maintain the water and electrolyte balance.
Zona fasciculate: It produces the glucocorticoids (corticosteroids) such as cortisol hormones.
Zona reticularis: It produces the androgen (sex hormones).
Inner medulla part: The medulla lies in the center of the adrenal gland and is dark brown in color. It secretes adrenaline into the blood stream in response to the stress. These hormones produce a ‘flight or fight’ response.
Blood supply: Each suprarenal gland receives three suprarenal arteries:
Superior suprarenal artery arise from the corresponding inferior phrenic artery. Middle suprarenal artery arise from the abdominal aorta. Inferior suprarenal artery arise from the corresponding renal artery.
Adrenogenital syndrome, Adrenalectomy, Cushing’s syndrome, Addision’s disease
Circle of Willis: It is an arterial anastomotic circle between the internal carotid and the vertebrobasilar system of arteries.
Anterior communicating artery connect- ing to left and right anterior cerebral arteries forms the anterior part of the circle of willis.
The lateral part is formed by the termination of internal carotid artery on each side.The circle is completed posteriorly by the bifurcation of basilar artery into the right and left posterior cerebral arteries.
Posterolateraly the posterior communicat- ing artery is the connecting link between the internal carotid and posterior cerebral arteries.
cerebellum the little brain, sits at the base of the brain in the posterior cranial fossa below the tentorium and behind the brainstem. three surfaces: anterior (petrosal), superior (tentorial), inferior (suboccipital)three fissures: primary (tentorial), horizontal (petrosal), prebiventral/prepyramidal (suboccipital)two hemispheres single median vermis
superior cerebellar artery (SCA): branch of the distal basilar artery
anterior inferior cerebellar (AICA): branch of the proximal basilar artery posterior inferior cerebellar (PICA): branch of the distal vertebral arteries
Connections to brainstem
to the midbrain via the superior cerebellar peduncles (brachia conjunctiva)
to the pons via the middle cerebellar peduncles (brachia pontis)
to the medulla via the inferior cerebellar peduncles (restiform bodies)
GREY MATTER OF CEREBELLUM It consists of the cerebellar cortex and the cerebellar nuclei. There are four pairs of nuclei:
1 Nucleus dentatus is neocerebellar. 2 Nucleus globosus 3 Nucleus emboliformis is paleocerebellar. 4 Nucleus fastigii is archicerebellar
Balance, Posture, Walking, Throwing a ball, Maintaining balance, Motor learning, Cognitive function: cerebellum also plays a part in higher-level cognitive functions, such as:
Attention, Language processing, Procedural memory (memory of how to perform tasks), Spatial reasoning
Emotional regulation:
Cerebellar dysfunction can manifest in various ways, depending on the affected area. Here are some common signs of cerebellum problems:
Tremors, Balance problems, Difficulty walking, Speech problems, Impaired coordination, Dizziness, Difficulty with motor learning
cerebrum: The cerebrum is very important part of the brain made by right and left cerebral hemispheres.Both the cerebral hemispheres are sepa- rated from each other by median longitudinal fissure. Each hemisphere contains a cavity called lateral ventricle. Occupy: It occupies anterior and middle cranial fossa and supratentorial part of the posterior cranial fossa. Gyri: The cerebral hemisphere have complicated folds called gyri. Sulci: The cerebral hemisphere have groove between gyri are called sulci. Ex. Fea. Two right and left cerebral hemisphere.Two hemisphere are incompletely separated from each other by the median longitunidal fissure.
Two hemisphere are connected to each other across the median plane by corpus callosum. Each hemisphere contains cavity called lateral ventricle. The surface area of cerebrum is 2000sqcm. Each lobe have Threes surfaces: (MIS)
1. Superolateral surface: Is convex and related to the cranial vault.2. Medial surface: It is flat and vertical.
It is separated from the corresponding surface of the opposite hemisphere by falx cerebri and longitudinal fissure 3. Inferior surface: It is irregular and divided into Anterior part: the orbital surface. Posterior part: the tentorial surface.The two parts are separated by a deep cleft called the stem of the lateral sulcus.
Four border: (SIMM)1. Superomedial border: It separates the Superolateral surface from medial surface.2. Inferiolateral border: It separates the Superolateral surface from inferior surface.The anterior part of this border is called superciliary border.There is a depression on the inferolateral border situated about 5cm in front of the occipital pole. It is called the preoccipital notch.3. Medial orbital
border: It separates the medial surface from orbital surface.4. Medial occipital border: It separates the medial surface from tentorial surface.Three poles1. Frontal: At the anterior end.2. Occipital: At the posterior end.3. Temporal: At the anterior end of the temporal lobe. Lobes of cerebrum: Each cerebral hemisphere is divided into 4 lobes- 1. Frontal 2. Parietal 3. Occipital 4. Temporal
कूर्च
षट् कूर्चाः ते हृस्त-पाद-ग्रीवा मेढठ्ठषु। हृस्तयोर्डों पादयोौँ, ग्रीवामेढट्ठयोरेकैकः।।(सु.शा. 5/13)
कूर्च खुरचनी के सामान होते है। सिरा, स्नायु, धमनी व पेशी का सन्त्रिपात जो कूंची (Brush) के सामान दिखाई देता है उसे कूर्च कहते है।
कूर्च छः होते है- हाथों में 2 ग्रीवा में 1 पैरों में 2 मेढ़ (मूत्रेन्द्रिया) में 1
कण्डरा (Tendon)
षोडश कण्डराः – तासा चतस्तः पादयोः तावत्थो हृस्त-ग्रीवा-पृष्ठेषु
अंगों का संकोच व विस्तार करने वाली बड़ी स्नायुओं को कण्डरा कहते है। हाथों और पैरों की कण्डराओं का निवेश नख है। ग्रीवा की कण्डराओं का निवेश मेद्र है। पृष्ठ की कण्डराओं का निवेश बिम्ब (Pelvis) है।
जाल (Plexus)मांस-सिरा स्नायुास्थि जालानि प्रत्येकं चत्वारि। (सु.शा. 5/12)
शरीर मे मांस, सिरा, स्नायु और से अस्थियों के समूह जिस स्थान पर एकत्र होकर एक जालिदार रचना बनाते है, उस स्थान को जाल कहते है। मांस, सिरा, स्नायु और अस्थि इन प्रत्येक से चार जाल होते है। यह मणिबंध और गुल्फ में आश्रित होते है। इस प्रकार मांसजाल एक, सिराजाल एक, स्नायुजाल एक तथा अस्थिजाल एक दोनों मणिबन्धों में चार-चार जाल बनाते है। इसी तरह दोनों गुल्फ में चार-चार जाल होने से शरीर में कुल 16 जाल होते है।
Hip Ligaments
1. Fibrous Capsule
The strong but loose fibrous capsule of the hip joint permits the hip joint to have the second largest range of movement. The capsule has two sets of fibers: Circular fibers form a collar around the femoral neck called zona orbicularis and the longitudinal fibers runs along the neck of femur and carry blood vessels.
2. Iliofemoral ligament
Iliofemoral ligament is the strongest ligament of the body.
It is the ligament of hip joint that runs between the ilium and the femur.
It has inverted Y shaped appearance, and prevents hyper extension of the hip joint.
Pubofemoral ligament
Pubofemoral ligament extend from iliopubic eminence and superior pubic ramus of hip bone up to the intertrochanteric line of the femur, deeper to the medial limb of the iliofemoral ligament.
It prevents the excessive abduction and extension of the thigh.
Ischiofemoral ligament
This ligament extend from body of the ischium just below the aceta- bulum up to the intertrochanteric line of femur deeper to the lateral limb of iliofemoral ligament. Some fibres of ischiofemoral ligament are twisted around the neck of femur, and reach the anterior attachment. This liga- ment gives support to the hip joint posteriorly.
It has spiral orientation and prevente hyperextension and holds femoral head in the acetabulum.
5. Ligament of the head of femur
It is also called round ligament of the femur, ligamentum teres femoris . the foveal ligament.
Its apex is attached to the fovea capitis on the head of femur and base is attached to transverse acetabular ligament and the margin of the acetabular notch (deficient part of acetabulum).
6 Transverse acetabular ligament
It is part of acetabular labrum which bridges the acetabular notch. It transmits acetabular vessels and nerves to the joint.
Blood supply
Obturator artery, Circumflex femoral artery (two)
Nerve supply
Femoral nerve, Superior gluteal nerve, Obturator nerve
Movements
Flexion Extension Abduction Adduction Medial rotation Lateral rotation Circumduction
सन्धयोष्टविधाः-कोरो-लूखल-सामुदद्र-प्रतर- तुन्नसेवनी – वायसतुण्ड – मण्डल शङ्खावर्त्त ॥(सु.शा. 5/31)
कोर-दरवाजें, खिड़कियों ; लूखल-उखली और मूसल : सामुदग—संपुट।
प्रतर सन्धि- प्रतर सन्धियों में दोनों अस्थियों के पृष्ठ समतल होते है तथा इनमें थोड़ी गति होती है। तुन्नसेवनी- सिलाई : वायसतुण्ड -कौबे की चोंच ;
; शंखावर्त – शंख के समान मण्डल सन्धि- यह तरूण अस्थियों की सन्धि है।
कंठनाडी, नेत्र आदि प्रत्यंगो में स्थित तरूण अस्थियों में आपस में जो सन्धि होती है,
