Morphology of the endocrine glands. Done by : Areej Al-Hadidi

Transcription

1 Morphology of the endocrine glands Done by : Areej Al-Hadidi

2 *nervous and endocrine systems work together &the nervous system control the endocrine *the nervous system is fast because of the action potential while the endocrine system is slow Note :please go back and read the table in slide 3 Exocrine glands secrete products into ducts which empty into body cavities or body surface sweat, oil, mucous, & digestive glands Endocrine glands secrete products (hormones) into bloodstream pituitary, thyroid, parathyroid, adrenal, pineal other organs secrete hormones as a 2nd function hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart & placenta *development of the exocrine and endocrine glands is the same at the beginning (invagination of the epithelium tissues,they connect with epithelium) *in exocrine glands the connection become duct body (cavities ) or into body surface and it empties either inside the *hormone secreting glands as pituitary,thyroid,parathyroid &adrenals are considered as complete organs Hypothalamus and Pituitary Gland Both are master endocrine glands since their hormones control other endocrine glands Hypothalamus is a section of brain above where pituitary gland is suspended from stalk *the hypothalamus receives inputs(sensory modality) from different parts (cortex,thalamus,limbic system &internal organs ) and according to the state of the body releases stimulatory or inhibitory hormones to control the pituitary gland * The pituitary gland influences the activities of many other endocrine glands. The pituitary gland itself is controlled by the hypothalamus

3 Pituitary gland *The pituitary gland is a small, pea shape structure attached to the undersurface of the brain by the infundibulum,the gland is well protected by virtue of its location in the sella turcica of the sphenoid bone directly above the sphenoid sinus. Because the hormones produced by the gland influence the activities of many other endocrine glands, the hypophysis cerebri is often referred to as the master endocrine gland. For this reason, it is vital to life. *the pituitary gland is divided into anterior and posterior lobes Anterior lobe = 75% develops from roof of mouth Posterior lobe = 25% ends of axons of 10,000 neurons found in hypothalamus neuroglial cells called pituicytes The pituitary is composed of two distinct lobes The anterior lobe or adenohypophysis (pars distalis, pars tuberalis and pars intermedia) The posterior lobe or neurohypophysis (pars nervosa, infundibular stalk or stem and median eminence) * the anterior lobe : 1.pars tuberalis it is a tube like structure,it is part of the infundibulum and it surrounds the stalk (stem)which also part of the infundibulum * pars tuberalis +stalk form the infundibulum * the infundibulum is attached directly to the pars nervosa in posterior lobe and it originates from the brain 2. pars distalis : it forms the major part 3.pars intermedia: it is almost rudimentary *the posterior lobe : 1.pars nervosa : this region constitutes the majority of the posterior pituitary, it stores and releases hormones

4 *it connects to the hypothalamus by the stalk 2. stalk : it is part of infundibulum 3. median eminence : it is more likely to be a part of hypothalamus rather than posterior lobe Relations: *the pituitary gland located in hypophysial fossa which is part of sella turcica *sella turcica is composed of ant wall,post wall & depressed area(hypophysial fossa) *anteriorly :tuberculum sella *inferiorly: sphenoid sinus *posteriorly: The dorsum sellae, the basilar artery, and the pons Superiolateral :ant and post clinoid processes which are surround the infundibulum *ant to tuberculum sella there is a sulcus called prechiasmatic sulcus, it optic chiasm contains *when optic nerves exit the optic canal and reach the cranial cavity,they will be connect to each other and form optic chiasm in the prechiasmatic groove Ant to prechiasmatic sulcus we can find the limbus of sphenoid *Optic chiasm located anterior superior to the gland *ant and post clinoid processes attach to extension of dura mater in meninges called diaphragma sellae *the diaphragm sellae covers the gland from superior part from the brain, it isolates the gland * The diaphragma sellae, which has a central aperture that allows the passage of the infundibulum.the diaphragma sellae separates the anterior lobe from the optic chiasma *cavernous sinus :part of venous sinuses *Laterally : cavernous sinus with its content *it contains nerves that will go to the orbit and these are : 1.the third branch of the cranial nerve(oculomotor)

5 2. the fourth branch of the cranial nerve (trochlear) 3. two branches of the fifth cranial nerve (ophthalmic and maxillary ) *all nerve above located in the lateral wall (outside) 4.the sixth cranial nerve (abducent) *the abducent nerve & internal carotid artery located in the medial wall(inside) *those nerves emerge directly from the brainstem toward the orbits by sup orbital fissure Note: maxillary nerve passes through foramen routundum *any problem in the pituitary gland can affect these structures *blood supply: *blood stream to the gland is very important because it is the way by which the hormones go to targeted region *it supplies by two arteries (branches from internal carotid artery) 1.inferior hypophysial artery for post pituitary gland 2. superior hypophysial artery for ant pituitary gland Hypophysial portal system: *portal system: means that there is two capillary beds instead of one,that is very important because the materials that come from hypothalamus must go to the ant lobe not to the heart *Artery arteriole primary capillary bed portal vein another capillary bed(secondary ) venule vein *the primary capillary bed located in the median eminence *The ant pituitary gland is controlled by hormones secreted from hypothalamus.. How??? *in median eminence releasing and inhibitory hormones enter the primary capillary bed and then travel through the portal vein to enter ant lobe at secondary capillary bed * The veins drain into the intercavernous sinuses.

6 *blood flow in post lobe: inferior hypophysial artery capillary bed posterior hypophysial vein *in neurohypophysis there is no cells to secrete hormones and it does not synthesize hormones *hormones are released by paraventricular nucleus &supraoptic nucleus *there is two hormones (antidiuretic hormone and oxytocin) act as neurotransmitters and they are stored in neurohypophysis Thyroid gland Largest endocrine gland in the body Location: Cervical region anteriorly Structure Two lobes Isthmus Pyramidal lobe Secretes two hormones Thyroid hormone (thyroxin & triiodothyronine) Increase tissue metabolism Calcitonin Lowers blood calcium *The thyroid gland consists of right and left lobes connected by a narrow isthmus *the gland is composed of : 1.lobe : Each lobe is pear shaped, with its apex being directed upward as far as the oblique line on the lamina of the thyroid cartilage; its base lies below at the level of the fourth or fifth tracheal ring.(c5-t1) 2. isthmus: It extends across the midline in front of the second, third, and fourth tracheal rings 3.pyramidal lobe:

7 Mostly found extending upward from the isthmus usually to the left of the midline *development of the gland from the mouth (mainly the tongue ),foramen cecum migrates downward anterioly toward the cervical region..reminant of this migration form the pyramidal lobe Connective tissue capsule surrounds thyroid gland From which connective tissue septa extend into the gland CT attaches the capsule to the cricoid cartilage & tracheal rings *capsule : dense irregular CT The visceral part of the pretracheal fascia surrounds the thyroid gland and attaches it to the trachea and larynx Called Capsule of pretracheal fascia or sheath of thyroid gland * pretracheal fascia is part of the deep cervical fascia *parathyroid gland outside the capsule but inside the sheath Fibromuscular band Connects the pyramidal lobe with the hyoid bone Levator glandulae thyroideae *In the development of the thyroid gland,it descends through thyroglossal duct, this duct will degenerates (sometimes it does not degenerate and remains as ligament called fibromuscular band) * fibrous or muscular band frequently connects the pyramidal lobe to the hyoid bone; if it is muscular, it is referred to as the levator glandulae thyroideae Relations: *it is almost superficial structure separated from the skin by infrahyoid muscles *anteriolateral: sternohyoid and sternothyroid *these muscles prevent swelling of the gland,swelling may occur anteriorly or posteriorly but not in this area * Posterolaterally: The carotid sheath with the common carotid artery, the internal jugular vein, and the vagus nerve *medially : The larynx, the trachea, the pharynx, and the esophagus. Associated with these structures are the cricothyroid muscle and its nerve supply, the external laryngeal nerve. In the groove between the esophagus and the trachea is the recurrent laryngeal nerve(it is posteriomedially)

8 *posteriorly: parathyroid glands Blood supply: Arteries Superior thyroid artery from external carotid Inferior thyroid artery from thyrocervical trunk * sup and inf thyroid arteries are the major supply and they are post to the gland Thyroidea ima (present in 10% of people) from brachiocephalic a. *it located ant to the trachea Arteries supplying thyroid gland anastomose with each other *The superior thyroid artery, a branch of the external carotid artery, descends to the upper pole of each lobe, accompanied by the external laryngeal nerve *The recurrent laryngeal nerve crosses either in front of or behind the inferior thyroid artery, or it may pass between its branches. Veins Superior thyroid vein drain into internal jugular vein Middle thyroid vein drains into internal jugular or inferior thyroid Inferior thyroid vein drains into the left brachiocephalic vein *sup and middle thyroid veins on both side (right and left) while the inf one found on the left side (2 branch to the left) to drain into left brachiocephalic vein *lymphatic drainage Prelaryngeal deep cervical Pretracheal Paratracheal deep cervical Paratracheal deep cervical Deep cervical (ultimate drainage) Innervations: Sympathetic trunk Superior, middle, & inferior cervical ganglia *innervations of blood vessels so it control the blood flow not secretion

9 *the presence or absence of sympathetic trunk determine if there is vasoconstriction or vasodilatation Parasympathetic? (if present,by vagi and recurrent laryngeal nerves ) Regulation through pituitary(control secretion) Thyroid Gland: Surface Anatomy Hyoid bone C3 Posterior to the mandible Laryngeal prominence (Adam s apple)- tip (C4) Cricoid cartilage C6 Cricothyroid ligament First tracheal cartilage Thyroid gland Isthmus 2nd 4th tracheal rings Lobe C5-T1 Development of Thyroid Gland Develop from an endodermal thickening at the ventral midline between arch I & II Thyroid diverticulum At foramen cecum Migrate caudally Thyroglossal duct Path of migration Obliterate and disappear Adult position Thyroid Gland Anomalies Remnants of thyroglossal duct Aberrant thyroid tissue Thyroglossal duct cysts Pyramidal lobe Parathyroid glands Small, oval endocrine glands Usually four glands (two superior & two inferior)

10 Secretes parathyroid hormone (parathormone) Elevates blood calcium levels *they develop from third and fourth pharyngeal pouches then they migrate,this migration cause a lot of irregularity in position Location: Lie on the posterior aspect of the lateral lobes of the thyroid gland Superior glands: Lower edge of cricoid cartilage Middle of the thyroid gland Inferior glands Lower pole of the thyroid gland Surrounded by a connective tissue capsule with septa dividing it into irregular lobes Lies external to the thyroid gland capsule (outside it ) Surrounded by the thyroid gland sheath Blood supply: Arteries Inferior thyroid a.(mainly) Superior thyroid a. Inf glands totally from inf thyroid artery while sup one both Veins Middle thyroid v. Inferior thyroid v. Lymphatic drainage Paratracheal deep cervical Pretrachial LN do not supply these glands because they are posterior Deep cervical Nerve supply middle, & inferior sympathetic cervical ganglia

11 *The two suprarenal glands are yellowish retroperitoneal organs that lie on the upper poles of the kidneys. They are surrounded by renal fascia (but are separated from the kidneys by the perirenal fat) *the right one is pyramidal in shape while the left one is crescent Relations: Right suprarenal gland :It lies behind the right lobe of the liver and extends medially behind the inferior vena cava. It rests posteriorly on the muscular part of the diaphragm. Left suprarenal gland: it extends along the medial border of the left kidney from the upper pole to the hilus,it lies behind the pancreas, the lesser sac, and the stomach and rests posteriorly on the diaphragm. Structure: *capsule,cortex and medulla : from outside to inside *cortex derived from mesoderm *medulla derived from ectoderm *there are three zones in the cortex(zona glomerulosa, zona fasciculate and zona reticularis *Each gland has a yellow cortex and a dark brown medulla. The cortex of the suprarenal glands secretes hormones that include mineral corticoids, which are concerned with the control of fluid and electrolyte balance; glucocorticoids, which are concerned with the control of the metabolism of carbohydrates, fats, and proteins; and small amounts of sex hormones, which probably play a role in the prepubertal development of the sex organs. The medulla of the suprarenal glands secretes the catecholamines epinephrine and norepinephrine.

12 Adrenal Medulla Chromaffin cells receive direct innervation from sympathetic nervous system sympathetic preganglionic axons pass, without synapsing, through the sympathetic trunk, greater splanchnic nerves and celiac ganglion into the adrenal medulla develop from same tissue as postganglionic neurons Produce epinephrine & norepinephrine Hormones are sympathomimetic effects mimic those of sympathetic NS cause fight-flight behavior Acetylcholine increase hormone secretion by adrenal medulla Blood supply: Arteries Inferior phrenic artery from aorta Aorta (suprarenal artery) Renal artery Veins Right suprarenal vein IVC Left suprarenal vein left renal vein *right renal vein is shorter than the left one so right suprarenal vein drains directly into IVC blood enters from capsular arteries which form 1. capillary plexuses in the zona glomerulosa 2. sinusoids in the zona fasiculata. The sinusoids branch again to form capillary plexuses in the zona reticularis and medulla. Then they drains to suprarenal veins This system is similar to that of the pituitary gland in that the blood that enters the medulla carries hormones secreted by the cortical cells Good luck