Anatomy of the Endocrine System

Anatomy of the Endocrine SystemHypothalamusThe hypothalamus is a part of the brain located superior and anterior to the brain stem and inferior to the thalamus. It serves many different functions in the nervous system, and is also responsible for the direct control of the endocrine system through the pituitary gland. The hypothalamus contains special cells called neurosecretory cells—neurons that secrete hormones:

Thyrotropin-releasing hormone (TRH) Growth hormone-releasing hormone (GHRH) Growth hormone-inhibiting hormone (GHIH) Gonadotropin-releasing hormone (GnRH) Corticotropin-releasing hormone (CRH) Oxytocin Antidiuretic hormone (ADH)

Pituitary GlandThe pituitary gland, also known as the hypophysis, is a small pea-sized lump of tissue connected to the inferior portion of the hypothalamus of the brain. Many blood vesselssurround the pituitary gland to carry the hormones it releases throughout the body. Situated in a small depression in the sphenoid bone called the sella turcica, the pituitary gland is actually made of 2 completely separate structures: the posterior and anterior pituitary glands.Pineal GlandThe pineal gland is a small pinecone-shaped mass of glandular tissue found just posterior to the thalamus of the brain. The pineal gland produces the hormone melatonin that helps to regulate the human sleep-wake cycle known as the circadian rhythm. The activity of the pineal gland is inhibited by stimulation from

the photoreceptors of the retina. This light sensitivity causes melatonin to be produced only in low light or darkness. Increased melatonin production causes humans to feel drowsy at nighttime when the pineal gland is active.

Thyroid GlandThe thyroid gland is a butterfly-shaped gland located at the base of the neck and wrapped around the lateral sides of the trachea. The thyroid gland produces 3 major hormones: 

Calcitonin Triiodothyronine (T3) Thyroxine (T4)

Parathyroid GlandsThe parathyroid glands are 4 small masses of glandular tissue found on the posterior side of the thyroid gland. The parathyroid glands produce the hormone parathyroid hormone (PTH), which is involved in calcium ion homeostasis. PTH is released from the parathyroid glands when calcium ion levels in the blood drop below a set point. PTH stimulates the osteoclasts to break down the calcium containing bone matrix to release free calcium ions into the bloodstream. PTH also triggers the kidneys to return calcium ions filtered out of the blood back to the bloodstream so that it is conserved.

Adrenal GlandsThe adrenal glands are a pair of roughly triangular glands found immediately superior to the kidneys. The adrenal glands are each made of 2 distinct layers, each with their own unique functions: the outer adrenal cortex and inner adrenal medulla.PancreasThe pancreas is a large gland located in the abdominal cavity just inferior and posterior to the stomach. The pancreas is considered to be a heterocrine gland as it contains both endocrine and exocrine tissue. The endocrine cells of the pancreas make up just about 1% of the total mass of the pancreas and are found in small groups throughout the pancreas called islets of Langerhans. Within these islets are 2 types of cells—alpha and beta cells. The alpha cells produce the hormone glucagon, which is responsible for raising blood glucose levels. Glucagon triggers muscle and liver cells to break down the polysaccharide glycogen to release glucose into the bloodstream. The beta cells produce the hormone insulin, which is responsible for lowering blood glucose levels after a meal. Insulin triggers the absorption of glucose from the blood into cells, where it is added to glycogen molecules for storage.

GonadsThe gonads—ovaries in females and testes in males—are responsible for producing the sex hormones of the body. These sex hormones determine the secondary sex characteristics of adult females and adult males.

ThymusThe thymus is a soft, triangular-shaped organ found in the chest posterior to the sternum. The thymus produces hormones called thymosins that help to train and develop T-lymphocytes during fetal development and childhood. The T-lymphocytes produced in the thymus go on to protect the body from pathogens throughout a person’s entire life. The thymus becomes inactive during puberty and is slowly replaced by adipose tissue throughout a person’s life.

List of Endocrine Diseases

The endocrine glands in the human body are the thyroid, parathyroid, adrenal and pituitary. The following diseases are categorized according to these glands.

Thyroid GlandThis is a list of endocrine disorders caused by hyposecretion or hypersecretion of hormones by the thyroid gland.Goiter - Enlargement of the thyroid glandHyperthyroidism - Increased secretion of thyroxine and tri-iodothyronine hormonesHypothyroidism - Deficiency of thyroxine and tri-iodothyronine hormones.Thyroiditis - Hashimotos thyroiditis is most commonThyroid cancer - Development of malignant tumors in the thyroid gland.Parathyroid GlandThese glands are in the neck behind the thyroid gland. These glands maintain calcium homeostasis in the body. Hence disorders of these glands are related to altered calcium metabolism which can be the reason for bone disorders as well. The disorders and diseases of this gland are as follows:Primary hyperparathyroidism - Hyper function of the parathyroid glands.Secondary hyperparathyroidism - Mostly caused due to hypercalcemia that afects the glands.Tertiary hyperparathyroidism - Hyperplasia of the parathyroid glands.Hypoparathyroidism - Decreased secretion of parathyroid hormones.Osteoporosis - It is bone disease caused due lack of minerals, especially calcium, when parathyroid gland does not function well.Rickets - It is seen in children due to lack of Vitamin D and calcium.Oseomalacia - It is a form of rickets observed in adults.Adrenal Gland

The adrenal glands are located above the kidneys in humans. These glands mostly secrete hormones that govern human behavior and moods, known as corticosteroids like cortisol, and catecholamines like epinephrine. The disorders of this gland are therefore mostly mood altering disorders, these are mentioned below.Addison's disease - It is caused due to hyposecretion of hormones by the adrenals.Conn's syndrome is caused due to an overproduction of aldosterone.Cushing's syndrome is a disorder is caused due to an increased secretion of cortisolPheochromocytoma is a tumor in the medulla of the adrenal glandsAdrenocortical carcinoma - It is a rare cancer of the adrenal glands.Pituitary GlandThis gland secrete the maximum number of hormones in the human body that regulate growth and development. Thus, the list of diseases caused due to an abnormal pituitary gland or alterations in secretion of any hormone are many.Diabetes insipidus is caused due to insufficient secretion of vasopressin secreted by the posterior pituitary gland.Hypopitutiarism - Decreased secretion of pituitary hormonesAcromegaly is caused due to an overproduction of growth hormone.Prolactinoma is a tumor that causes increased secretion of prolactin.Sex hormone disorders - Pituitary gland secretes various sex hormones, thus altered secretion of these affects the sexual development or regulation of sexual characteristics.

Nervous system: set of nerves, ganglions and nervous centers that receive sensory signal. Commands and coordinates vital functions.Brachial plexus: network of nerves of the arm.Intercostal nerve: cord conducting nerve impulses between the ribs.Radial nerve: cord conducting nerve impulses in the area of the radius.Median nerve: main cord conducting nerve impulses in the upper limb.Ulnar nerve: cord conducting nerve impulses in the area of the elbow.Lumbar plexus: network of nerves of the lower back.Sciatic nerve: cord conducting nerve impulses in the area of the thigh and lower leg.Common peroneal nerve: cord conducting nerve impulses along the inside of the lower leg.Superficial peroneal nerve: cord conducting nerve impulses of the muscles and skin of the leg.Digital nerve: cord conducting nerve impulses of the fingers.Sacral plexus: network of nerves of the sacrum.Spinal cord: substance belonging to the nervous system, found in the holes of the vertebrae.Cerebellum: nervous centre situated under the brain.Cerebrum: seat of the mental capacities.

List of Nervous System Diseases

Nervous system disorders are broadly classified as:

Encephalitis: Disorder characterized by inflammation of the brain.Meningitis: Results in inflammation of membranes of the brain.Tropical Spastic Paraparesis: Disease affecting the bone marrow, also results in Leukemia in some cases.Arachnoid Cysts: Cyst formation on parts of brain or spinal cord.Huntington’s Disease: Results in degeneration of the brain cells.Alzheimer’s: A neuron-degenerative disorder.Locked-in Syndrome: Clinical condition resulting in paralysis due to the damaged pons.Parkinson’s: Neurological disorder affecting speech and skills.Tourette’s: Genetic disorder, often surfaces during childhood.Multiple Sclerosis: Resulting from the damage of myelin sheath of the neuron cells.Causes of Nervous System Diseases

The main causes of neurological disorders are:

TraumaInfectionsDegenerationStructural defectsTumorsAutoimmune DisordersStrokeMedication Side EffectsGenetic DisordersThese conditions disorder the nervous system and contribute to abnormal behavior of various body organs.Symptoms of Nervous System Diseases

The symptoms vary from diseases to diseases. However, some of the general symptoms include:

Continuous headacheLoss of sense and feelingLoss of memoryLoss of body and muscle strengthTremorsDefects in speechSeizuresSlow movement of body parts

SkullThe skull is composed of 22 bones that are fused together except for the mandible. These 21 fused bones are separate in children to allow the skull and brain to grow, but fuse to give added strength and protection as an adult. The mandible remains as a movable jaw bone and forms the only movable joint in the skull with the temporal bone.

Hyoid and Auditory OssiclesThe hyoid is a small, U-shaped bone found just inferior to the mandible. The hyoid is the only bone in the body that does not form a joint with any other bone—it is a floating bone. The hyoid’s function is to help hold the trachea open and to form a bony connection for the tongue muscles.VertebraeTwenty-six vertebrae form the vertebral column of the human body. They are named by region:

Cervical  (neck) - 7 vertebrae Thoracic  (chest) - 12 vertebrae Lumbar   (lower back) - 5 vertebrae Sacrum  - 1 vertebra Coccyx  (tailbone) - 1 vertebra

Ribs and SternumThe sternum, or breastbone, is a thin, knife-shaped bone located along the

midline of the anterior side of the thoracic region of the skeleton. The sternum connects to the ribs by thin bands of cartilage called the costal cartilage.Pectoral Girdle and Upper LimbThe pectoral girdle connects the upper limb (arm) bones to the axial skeleton and consists of the left and right clavicles and left and right scapulae.Pelvic Girdle and Lower LimbFormed by the left and right hip bones, the pelvic girdle connects the lower limb (leg) bones to the axial skeleton.

SKELETAL SYSTEM DISEASES

ArthritisArthritis is an inflammatory condition that affects your joints, such as the knees, or a portion of your spinal column. Typical symptoms of this condition include joint pain, swelling and stiffness accompanied by a reduction in the ability to freely move your joints. Osteoarthritis and rheumatoid arthritis are the most common types of this disease.Sponsored Links

Chronic Fatigue SyndromeThe Cfids Association of America Learn more about CFS.www.cfids.org/

Bone CancerBone cancer, though uncommon, is cancer that originates within a bone of your body causing bones to weaken. Individuals with bone cancer may experience fatigue, bone pain or frequent bone fractures.Though any bone can be affected by cancer, bone cancer most frequently occurs in longer bones, such as those in your legs or arms.LeukemiaLeukemia is a form of cancer that originates in the bone marrow and affects the lymphatic system. This disease results in the formation of abnormal, malfunctioning white blood cells, which interferes with the ability of your body to fight infection. There are four major types of leukemia: acute lymphocytic leukemia, chronic lymphocytic leukemia, acute myelogenous leukemia and chronic myelogenous leukemia.Osteomalacia (Rickets)Osteomalacia is a disease that leads to a softening and weakening of your bone tissue. This disease, which in children is also called rickets, is typically caused by prolonged vitamin D deficiency.OsteoporosisOsteoporosis is a condition in which bones become brittle and weak due to the extensive loss of bone tissue. Though the cause of osteoporosis is poorly understood, researchers believe that the bone remodeling process that occurs in healthy individuals is interrupted in individuals with this disease. Osteoporosis also commonly results in bone fractures of the wrist, spine or hip, which can even be caused by mild stresses such as coughing.Spina BifidaSpina bifida is a genetic birth defect that effects the development of the spinal cord while a baby is in the uterus. When present, this defect is typically detected and treated before a baby is born.

However, babies that are not treated before birth may be born with excess fluid in or around the brain. There are two major types of spina bifida: spina bifida occulta and spina bifida manifesta.Spinal CurvaturesThere are three main types of spinal curvatures: kyphosis, hyperlordosis and scoliosis.

Kyphosis---also called hunchback---is a deformity of the upper portion of the spinal column that results in severe forward bending of the spine. In children and adolescents, this condition may result from poor posture (postural kyphosis), misshapen vertebrae (Scheuermann kyphosis) or problems during fetal development (congenital kyphosis). In adults, this condition is often the result of another disease, such as rheumatoid arthritis, osteoporosis or cancer.

Functions of Muscular System:Muscular system has the following important functions in human body;

1. MOVEMENTS OF BODY PARTS: Skeletal muscles are responsible for all voluntary movements of human body parts. They provide the force by contracting actively at the expense of energy. In other words, muscles are motors of body where chemical energy of food is converted into mechanical work.

2. STABILITY AND POSTURE: Skeletal muscles stabilize human skeleton and give a proper posture to human beings. Some joints of human body are weak and they require the support of muscular

system to achieve stability. Skeletal muscles are very important for such joints.

3. HEAT PRODUCTION: A large share of body’s energy is used by muscular system. As a result of high metabolic rate, muscles produce great amount of heat in the body. Heat produced by muscles is very important in cold climates.

4. CIRCULATION: Cardiac muscles provide the main force for circulation of blood throughout human body. The regular pumping of heat keeps the blood in motion and nutrients are readily available to every tissue of human body.

5. HELP IN DIGESTION: Smooth muscles of organs like stomach and intestine help the digestive system in the process of digestion of food.

Muscular System Anatomy

Muscle TypesThere are three types of muscle tissue: Visceral, cardiac, and skeletal.

1. Visceral Muscle. Visceral muscle is found inside of organs like the stomach, intestines, and blood vessels. The weakest of all muscle tissues, visceral muscle makes organs contract to move substances through the organ. Because visceral muscle is controlled by the unconscious part of the brain, it is known as involuntary muscle—it cannot be directly controlled by the conscious mind. The term “smooth muscle” is often used to describe visceral muscle because it has a very smooth, uniform appearance when viewed under a microscope. This smooth appearance starkly contrasts with the banded appearance of cardiac and skeletal muscles. 

2. Cardiac Muscle. Found only in the heart, cardiac muscle is responsible for pumping blood throughout the body. Cardiac muscle tissue cannot be controlled consciously, so it is an involuntary muscle. While hormones and signals from thebrain adjust the rate of contraction, cardiac muscle stimulates itself to contract. The natural pacemaker of the heart is made of cardiac muscle tissue that stimulates other cardiac muscle cells to contract. Because of its self-stimulation, cardiac muscle is considered to be autorhythmic or intrinsically controlled. 

The cells of cardiac muscle tissue are striated—that is, they appear to have light and dark stripes when viewed under a light microscope. The arrangement of protein fibers inside of the cells causes these light and dark bands. Striations indicate that a muscle cell is very strong, unlike visceral muscles. 

The cells of cardiac muscle are branched X or Y shaped cells tightly connected together by special junctions called intercalated disks. Intercalated disks are made up of fingerlike projections from two neighboring

cells that interlock and provide a strong bond between the cells. The branched structure and intercalated disks allow the muscle cells to resist high blood pressures and the strain of pumping blood throughout a lifetime. These features also help to spread electrochemical signals quickly from cell to cell so that the heart can beat as a unit. 

3. Skeletal Muscle. Skeletal muscle is the only voluntary muscle tissue in the human body—it is controlled consciously. Every physical action that a person consciously performs (e.g. speaking, walking, or writing) requires skeletal muscle. The function of skeletal muscle is to contract to move parts of the body closer to the bone that the muscle is attached to. Most skeletal muscles are attached to two bones across a joint, so the muscle serves to move parts of those bones closer to each other. 

Skeletal muscle cells form when many smaller progenitor cells lump themselves together to form long, straight, multinucleated fibers. Striated just like cardiac muscle, these skeletal muscle fibers are very strong. Skeletal muscle derives its name from the fact that these muscles always connect to the skeleton in at least one place.Gross Anatomy of a Skeletal MuscleMost skeletal muscles are attached to two bones through tendons. Tendons are tough bands of dense regular connective tissue whose strong collagen fibers firmly attach muscles to bones. Tendons are under extreme stress when muscles pull on them, so they are very strong and are woven into the coverings of both muscles and bones.Muscles move by shortening their length, pulling on tendons, and moving bones closer to each other. One of the bones is pulled towards the other bone, which remains stationary. The place on the stationary bone that is connected via tendons to the muscle is called the origin. The place on the moving bone that is connected to the muscle via tendons is called the insertion. The belly of the muscle is the fleshy part of the muscle in between the tendons that does the actual contraction.

MyotoniaThe National Institute of Neurological Disorders and Stroke (NINDS) says that myotonia is a medical problem in which the muscles relax slowly after contraction or stimulation. 

Specific symptoms of myotonia include trouble releasing a grip on a certain object such as a cup or spoon, trouble walking and difficulty getting up from a chair. 

Myotonia can be inherited or it can just develop over time. Cold weather can serve as a trigger for myotonia. Alterations in specific sodium and potassium channels that control muscle contraction and relaxation are to blame for myotonia. 

The NINDS says that treatment for myotonia includes taking medications such as quinine,

mexiletine, phenytoin and other anticonvulsant medications to help manage myotonia. Physical therapy can also be utilized to help in strengthening muscles.Sponsored Links

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Mitochondrial MyopathiesMitochondria refer to tiny structures in cells that provide energy. According to the NINDS, mitochondrial myopathies refer to a neuromuscular disease in which there is damage to the mitochondria. 

Specific symptoms of mitochondrial myopathies include muscle weakness, heart rhythm abnormalities, heart failure, deafness and blindness. Mitochondrial myopathies can also lead to vomiting, drooping eyelids, seizures and dementia. The NINDS says that muscle cramping is rare. A headache, nausea and difficulty breathing are additional symptoms of mitochondrial myopathies. 

As in myotonia, no specific treatment exists for mitochondrial myopathies. Physical therapy can help maintain range of motion and supplements such as riboflavin, coenzyme Q and carnitine might help manage mitochondrial myopathies.

Myofascial Pain SyndromeMyofascial pain syndrome is a chronic disorder affecting one or more muscle groups. According to StopPain.org, produced by the Albert Einstein College of Medicine, myofascial pain syndrome is characterized by burning, aching and nagging pain. Sometimes pain can move from the muscle to other regions of the body such as the shoulder. This is known as referred pain.

Parts of the Integumentary System

SkinThe skin is the most important organ of the body, as it protects the delicate organs of the body. The skin is divided into three separate layers as follows:

Epidermis: This is the outermost layer of the skin that contains four separate layers of epithelial tissue. The outer most layer is the stratum corneum that is about 2 to 30 cells thick. These are keratinized and dead cells that make the skin waterproof! The second and third layer consists of the stratum granulosum and stratum lucidum, which contain cells that are not keratinised as yet. As these skin grows, the cells are pushed outward and come towards the surface. The last and the deepest layer of the epidermis is the stratum germinativum. These cells are active mitotically and have the ability to reproduce, as these cells are living, thus, making them the manufacturing center for growing skin.Dermis: The dermis lies immediately after the epidermis. The dermis consists of its own blood supply and thus contains many complex structures. The sweat glands are present in this layer that collect waters and waste products from the blood stream. This waste is excreted from the pores in the epidermis along with the water in form of sweat. The hair roots are also present in this layer that help in the growth of hair. When the hair reaches outside the epidermis, the cells are dead. The connective tissue made of collagen fibers are also found in the dermis that help give the skin elasticity and strength.

Subcutaneous Layer: The last layer of the skin containing the adipose tissues, cushions the delicate organs beneath the skin. The body temperature is also maintained within this layer by insulating the body to the temperature fluctuations.

Functions of the Skin

Thermoregulation: The thermoregulation of the skin is carried out with the help of evaporation of the sweat and regulation of the blood flow to the dermis.Sensations: The cutaneous sensations like touch, pressure, vibration, pain, cold, hot, etc, are felt by the skin.Protection: The protective barrier of the skin helps prevent diseases, infections, dehydration, etc.Production of Vitamin D: The precursor present in the skin and UV rays, helps in the production of vitamin D, an important nutrient of the body.Healing: When the epidermis breaks away due to a minor cut or burn, the cells on the lower layers of the skin migrate upwards as a sheet. When two ends of the sheet meet, the cells stop growing due to a process called 'contact inhibition'. Thus, the epidermis is sealed and the skin returns to normal.HairHair, feathers, scales, etc. are all derived from the skin. In case of humans, the hair extends to the surface from the hair roots or hair bulbs present in the dermis. The functions of the hair include protection and sensation to touch. Hair is made up of dead, keratinized cells that are bound together with the extracellular proteins. Each hair is divided into hair shaft that is the superficial layer and the root that is in the dermis. Hair follicle is the structure that surrounds the hair root. The oil glands present around the hair follicles help keep the hair and the surrounding skin moist. It also acts as a protective organ involved in temperature regulation.

Arrector Pili Muscles

These are smooth muscle cells that extend from the hair follicle till the papillary layer of the dermis. These arrector pili muscles cause the hair to become erect and give the feeling of 'goose bumps'. Hair can trap more warm air when they are erect. Hence, during extreme cold environment, these muscles contract leading to erect hair. Under conditions of high temperature, the arrector pili muscles relax so that the hair lie flat on the skin and thus aid in the escape of heat.

Nails

Nails, claws and horns are structures that are derived from the skin. The nail is a highly keratinized structure of modified epidermal cells. The nail bed gives rise to nails, that is thickened to form a lunula. The moon shaped structure that you observe at the base of your nails is called the lunula. The function of nails is to help in grasping and holding things. The nails act as counter force and help increase the sensitivity of the fingertip. They also protect the fingertips and underlying tissues from damage.

Sebaceous Glands and Nerves

Sebaceous glands secrete the oil coating for the hair shaft. When these sebaceous glands become clogged with dirt and microorganisms, they become infected and cause pimples or acne. The complex network of the nerves present all over the skin helps send and receive important impulses to and from the brain, thus playing a vital role in sense of touch.

Sweat Glands

Sweat glands have an opening through the skin pores, and they help in excretion of water and electrolytes. Eccrine sweat glands are found all over the body whereas apocrine sweat glands are present in armpits and groin. Eccrine glands are involved in the cooling mechanism of thermoregulation whereas, apocrine glands are involved in the secretion of chemicals and pheromones.