Gross Morphology of the Endocrine Glands

Transcription

1 Gross Morphology of the Endocrine Glands A Pituitary Gland (Hypophysis Cerebri) Hypo means below, and physis means growth, so it is the gland that grows from below because it is located below the brain. It has an oval structure that s located beneath the hypothalamus and It attaches to it by a stalk we call it (infundibulum; it means funnel shaped). If we go back to the first year, we divided the brain into 3 parts (forebrain, midbrain and hindbrain), the forebrain is composed of cerebrum and diencephalon (it means two things hidden by the cerebrum) and the diencephalon consists of the thalamus (it means the chamber) and below it we can see the hypothalamus. The main function of the hypothalamus is the integration between the nervous system and the endocrine system. The pituitary gland is known as the master endocrine gland because it influences the activity of other endocrine glands in our body (by secreting hormones), and those hormones are: 1. Thyroid stimulating hormones (TSH); it influence the activity of the thyroid gland. 2. Adrenocorticotropic hormone (ACTH); it influence the activity of the adrenal gland. 3. Follicular stimulating hormone (FSH). 4. Luteinizing hormone (LH). These two hormones will influence the activity of the gonads (testis and ovaries). However, to make it clear let s imagine that the pituitary gland is the prime minister, and so the )رئيس الدولة ) hypothalamus thus it has a president who is the,(رئيس الوزراء) hypothalamus has the superiority over the endocrine system. 1

2 ; The location of pituitary gland It is located in the cranial cavity within the Sella turcica (Means the Turkish saddle) of the sphenoid bone. It is made of three parts: The anterior part (tuberculum sellae); it is the anterior horn of the saddle. Pituitary fossa or hypophyseal fossa where the gland is located. Dorsum sellae; it is the back of the saddle. In addition to these parts there is something we call it clinoid processes (bed post السرير (حواف of the Sella turcica. The Sella turcica looks like the bed where the pituitary gland is sleeping, however the post of the bed will be these clinoid processes (2 anterior and 2 posterior), they are very important because they provide an attachment for the sheet او اللحاف) (الغطاء which covers the pituitary and this sheet is a part from the dura matter we call it sellar diaphragm. (The sellar diaphragm of dura which covers the pituitary should attach to these clinoid processes). ; Divisions of Pituitary Gland The pituitary gland is made of two parts: 1. The anterior lobe (we call it adeno-hypo-physis): Adeno means gland so it is the glandular part of the pituitary. It constitutes about 75% of the weight of the gland. 2

3 2. The posterior lobe (we call it neuro-hypo-physis): It is more nervous in nature. It constitutes about 25% of the gland. It is a down growth from the hypothalamus, it does not secret hormones, but it stores hormones that s why it is very rich in axon terminals of nerve cells (more than 10,000 neurons in the hypothalamus will send their axons to end up in the posterior lobe). So the hormones that are secreted from the hypothalamus will be transported by vesicles down to the neurohypophysis to be stored. ; Development of Pituitary Gland Adenohypophysis: It is developed from ectodermal outgrowth or invagination (we call this outgrowth Rathke s Pouch) in the roof of the primordial mouth which we call it stomatodeum or stomodeum. During the 3 rd week of the embryological development the ectodermal cells in the roof of the stomodeum starts to invaginate upward producing a pouch, this pouch is called Rathke s Pouch. As Rathke s Pouch develops upward towards the brain (cranially), it elongates, and by the 5 th week of development the pouch will become disconnected from the primordial mouth. Once it is disconnected from the stomodeum it becomes like a small cyst (an ectodermal covering and a space inside it), the ectodermal covering of this cyst especially the ones in the anterior part will start to proliferate filling the space. By the end of the 5 th week and the beginning of the 6 th week the space will be completely filled so know it is not anymore a cyst, it is a sphere of cells. 3

4 The anterior part where the anterior cells proliferate and occupy the space will become the anterior part of the gland or pars anterior or pars distalis (since it is the distal part) Sometimes, a remnant of the space (a small cleft) remains there, we call it Rathke s cleft (not always present), if it is present, it will demarcate the border between the anterior ectodermal cells that proliferate and the posterior ectodermal cells of the cyst, these posterior cells will become what s known as pars intermedia (because it is located in the middle between pars distalis and pars nervosa which is a part of the neurohypophysis). As the ectodermal cells proliferate backward to fill the space, they also grow up upward to cover the infundibulum (pituitary stalk), once they cover it anterio-laterally we call them pars tuberalis. So the adenohypophysis will be divided into: 1. Pars anterior or distalis. 2. Pars intermedia. 3. Pars tuberalis. However, pars tuberalis and pars distalis have similar cells (the ectodermal cells from the anterior part), while pars intermedia has the remnant cells of the posterior ectodermal cells of the rathke s cyst. Neurohypophysis: At the same period of time when the adenohypophysis develops, there will be a downward growth from the hypothalamus that starts as a bud (we call it neurohypophyseal bud), this bud will elongate also but this time downward instead of upward and by the end of the 5 th week it will elongate to become behind the rathke s cyst. However, this hypophyseal elongation is not separated from the hypothalamus, it remains connected to the hypothalamus, so it will be divided (the neurohypophysis) into: 1. Pars nervosa (the nervous part). 2. The infundibulum or the pituitary stalk (the connection remains between the posterior pituitary and the hypothalamus). 4

5 ; The functions of the pituitary gland The anterior pituitary: secrets several hormones that controls the activity of the other endocrine glands (the first 4 hormones mentioned previously) and other three hormones which are: 1. Somatotropin hormone (growth hormone); which is required during the juvenile period for growth and during adult period for repair and regeneration of tissues. 2. Prolactin hormone; stimulate the production of milk by mammary glands. 3. Melanocyte stimulating hormone: it stimulates the melanocyte to proliferate. The posterior part: it does not synthesize hormones it stores hormones which are: 1. Oxytocin. 2. ADH (antidiuretic hormone) or vasopressin. This histological view shows you the difference, here is the pars nervosa totally separated part. And we can see a demarcating line here which demonstrate the cells of pars intermedia. Also, we can see here the cells of pars distalis. The cells of pars intermedia are the ones that secrete the melanocyte stimulating hormone, while the cells of pars distalis will secrete the remaining hormones. 5

6 ; Relations to Pituitary Gland It is very important especially during doing any surgery in the cranial base of the skull. Anteriorly: the tuberculum sellae and the sphenoidal air sinus. Posteriorly: the dorsum sellae, basilar artery and the pons. Superiorly: sellar diaphragm and the optic nerve (2 nd cranial nerve) or optic chiasma. Inferiorly: the hypophyseal fossa and the sphenoidal air sinus. Laterally: cavernous sinus (very large structure it contains cranial nerves III (oculomotor), Any adenoma or adenocarcinoma IV (trochlear), VI (abducent), two divisions of the occurs in the pituitary gland, as it trigeminal nerve (V) which are ophthalmic and enlarges, it will start to penetrate maxillary and internal carotid artery). In addition to into the cavernous sinus, which the cavernous sinus on each side the two cavernae become a very serious condition. (one on the left and one on the right) are connected to each other by small veins (anterior to The part of dura that surrounds the pituitary and posterior to it) those are called the the cerebrum we call it tentorium inter-cavernous sinuses they are very Important cerebelli. because they are the drainage site of the veins that draining the pituitary gland. 6

7 ; The vasculature of the pituitary gland In the pituitary gland we have something unique called the hypophyseal portal system. In portal systems in general, the blood will flow from one capillary network through a vein to a second capillary network, and then it will drain into the venous circulation, so the portal vein is always located between two capillary networks. In the hypophyseal portal system the arteries that supply the adenohypophysis (anterior lobe) will receive the blood supply from the Superior hypophyseal arteries coming from the internal carotid artery, we call them superior because they go superior to the pituitary (they actually go to the hypothalamus), and in the hypothalamus they will form the first capillary network, we call it the first hypophyseal plexus, in this plexus the blood will drain from the hypothalamus down through the portal veins, these portal veins will go into the adenohypophysis (anterior surface of the pituitary), then they will form the second plexus we call it the secondary hypophyseal plexus, and from there they will continue as the anterior hypophyseal veins that will go and drain into the anterior intercavernous sinus. This portal system is only associated with the anterior pituitary gland because there is an influence from the hypothalamus on the pituitary so this will permit the hypothalamic hormones (from hypothalamus) to act immediately on the anterior Pituitary cells before being diluted or destroyed in the systemic circulation. One example is the thyroid releasing hormone secreted from hypothalamus that goes to the first plexus then through the portal veins to the second plexus in the anterior pituitary gland, then they will bind to its receptors on the adenohypophyseal cells to stimulate them to secrete thyroid stimulating hormone, this hormone will go through the anterior hypophyseal veins to the circulation. 7

8 In the posterior lobe because its main function is storage and it is connected directly to the hypothalamus, we don t need portal circulation, because of that, the arteries will go directly from below forming what we call the inferior hypophyseal arteries (branch from internal carotid), then they will form a plexus that s called the infundibular plexus, this plexus will drain posteriorly onto the posterior inter-cavernous sinus. A Adrenal (Suprarenal) Glands It is a yellowish primary retroperitoneal organ that is located on the upper part of both kidneys. Made of two parts: 1. Cortex (the outer part) Constitutes about 85% of the gland (so it s the major part) Divided into 3 zones (from outside to inside): Zona glomerulosa (contains spheres of cells) This zone secretes hormones that control the menials in the body, these hormones are mineralocorticoids as aldosterone. Zona fasciculata (contains bundles or cords of cells) This zone secretes hormones that control glucose metabolism we called them glucocorticoids as cortisol. Zona reticularis (contains network of cells) This zone secretes hormones that control the growth of the gonads in the pre-pubertal period we call them androgens. 2. Medulla (inner part) Constitutes about 15 % of the gland. It is considered as a modified sympathetic ganglion area so it originates from the neural crest (the nervous system). Androgens in the adult period in females are responsible for testosterone production, while in males they are responsible for production of some androgens that are responsible for the masculinity. 8

9 Its main function is hormones secretion, which are: Epinephrine. Norepinephrine. These hormones are responsible for the sympathetic response (fight or flight). The fight or flight response is also called the five Fs response, they are related to the age and gender and they include: Fight (seen in males) Flight (seen in males) Freeze (seen in children) Fright (seen in females) Faint (seen in females) ; Coverage & Attachments of Suprarenal Glands The adrenal glands are covered by the renal fascia (the deep fascia covering the kidneys). In this figure, we can see the layers covering the kidneys, which are pararenal fat from the outside then we have the renal fascia and finally deep perirenal fat layer (between the renal fascia and the kidney), so the suprarenal gland here is covered by the renal fascia and this fascia is responsible for the attachment of the adrenal glands posteriorly to the diaphragm (to the crura of the diaphragm), so this is the major attachment. 9

10 Actually the adrenal glands are held in their position by their attachment to the crura of the diaphragm not to the kidneys, they are separated from the kidneys by the perirenal fat. Left Suprarenal Gland Crescent in shape (semilunar) More medial Larger The relations: Anteriorly: the pancreas, the lesser sac and the stomach. Posteriorly: the left crus of the diaphragm. ; Vasculature of the Suprarenal Glands Arterial Blood Supply, The blood supply to the adrenal glands is from 3 main arteries: Right Suprarenal Gland Pyramidal in shape (as a cap) More apical (at the superior pole of the kidney) Smaller The relations: Anterio-laterally: the liver. Anterio-medially: inferior vena cava (we have to retrace the IVC to see the gland) Posteriorly: the right crus of the diaphragm. 1. Superior suprarenal arteries 6-8 in numbers Come from the inferior phrenic artery, which is come from the abdominal aorta. 2. Middle suprarenal arteries Come from the lateral aspect of the abdominal aorta. 10

11 At the level of L1 (it is adjacent to the superior mesenteric artery not the celiac trunk, so in this picture the position is wrong). Important 3. Inferior suprarenal artery Come from the renal arteries These arteries before they reach to the adrenal glands they will branch to multiple branches, sometimes we can find more than 50 branch entering into the adrenal gland (there is no hilum for the arteries). The hilum of the gland can only be distinguished for the veins and nerves. Venous Drainage, We have only one vein for each gland which are: 1. Right suprarenal vein Shorter. Drains directly to the IVC. 2. Left suprarenal vein Longer. Drains to the left renal vein and goes with it to the IVC. If we look carefully to the figure we will see that the left suprarenal vein joins with the left inferior phrenic vein, so we should be careful when you want to ligate the left suprarenal vein, we should ligate above the junction (closer to the gland not to the renal vein). Lymph Drainage The lymph flows along with the kidneys into the para-aortic lymph nodes then to the cisterna chyli then to the thoracic duct finally to the venous circulation. Transformers Team A 11