Master of glands

Hipofisis, organ kecil yang menjuntai di bawah dasar otak, adalah sebuah kelenjar yang banyak berperan dalam aktivitas berbagai hormon. Kelenjar yang hanya berbobot 0,5 gr ini terlindung dalam ruang yang dikenal sebagai sella tursika atau fossa hipofisis di dasar tengkorak. Hipofisis terdiri atas 2 lobus, anterior dan posterior dan secara anatomis berhubungan langsung dengan hipotalamus. Hipotalamus sendiri terbagi atas 3 zona yaitu lateral, medial dan paraventrikuler. Magnocellular neurosecretory cells, salah satu kelompok sel pada zona paraventrikuler hipotalamus, memiliki axon yang berjalan turun ke hipofisis lobus posterior.
            Magnocellular neurosecretory cells, melepaskan 2 macam neurohormon, oksitosin dan vasopresin ke dalam sirkulasi. Oksitosin dilepaskan saat proses persalinan dan menyeba
bkan uterus berkontraksi. Hormon ini juga menstimulasi keluarnya air susu dari kelenjar mammae. Oksitosin juga dapat dilepaskan dengan sensasi somatik yang diakibatkan oleh hisapan bayi saat sedang disusui. Vasopresin, juga disebut dengan antidiuretic hormone (ADH) berperan dalam regulasi cairan dan osmolaritas. Dalam keadaan dehidrasi di mana volume darah menurun dan osmolaritas meningkat, vasopresin akan dilepaskan dan akan memerintahkan ginjal untuk meretensi cairan dan mengurangi produksi urin.
            Tidak seperti lobus posterior, lobus anterior hipofisis adalah kelenjar yang menghasilkan bermacam-macam hormon yang bertugas meregulasi sekresi hormon-hormon kelenjar lain. Kelenjar-kelenjar berikut ini bekerja di bawah pengaruh hipofisis: gonad, adrenal, tiroid dan mammae. Sedemikian luasnya peran hipofisis membuat kelenjar ini mendapat julukan “Master of Gland”. Meskipun demikian, hipofisis anterior tetap di bawah kontrol hipotalamus yang diperankan oleh parvocellular neurosecretory cells di zona paraventrikuler.
Berikut ini adalah hormon yang dihasilkan oleh hipofisi lobus anterior dan efek yang ditimbulkannya.

Hormon
Target
Efek
Follicle-stimulating hormone (FSH)
Gonad
Ovulasi, spermatogenesis
Luteinizing hormone (LH)
Gonad
Ovulasi, maturasi sperma
Thyroid-stimulating hormone (TSH) atau thyrotropin
Tiroid
Sekresi tiroksin (meningkatkan metabolisme)
Adrenocoticotropic hormone (ACTH) atau corticotropin
Korteks adrenal
Sekresi kortisol
Growth hormone (GH)
Semua sel
Stimulasi sintesa protein
Prolaktin
Mammae
Produksi dan sekresi air susu

            Hipotalamus berkomunikasi dengan lobus anterior hipofisis melalui hormon yang dilepaskan ke pembuluh darah kecil yang berjalan turun ke hipofisis anterior melalui tangkai hipofisis. Hubungan yang demikian ini dikenal sebagai hypothalamo-pituitary portal circulation. Hormon yang dilepaskan adalah sebagai berikut:

Thyrotropin releasing hormone (TRH) = TSH-RH
Corticotropin releasing hormone (CRH)
Gonadotropin releasing hormone (GnRH) = LH-RH
Growth hormone releasing hormone (GH-RH)
Growth hormone release inhibiting hormone (GH-RIH) = somatostatin
Prolactin releasing factor (PRF)
Prolactin release inhibiting factor (PIF)
Melanocyte stimulating hormone releasing factor (MSH-RF)
Melanocyte stimulating hormone release inhibiting factor (MSH-RIF)

            Hormon-hormon tersebut dikenal sebagai hypophysiotropic hormone. Apabila hormon hormon ini dilepaskan akan terjadi perubahan besar baik dalam fisiologi tubuh maupun otak manusia. Sebagai contoh, dalam kondisi stress psikis, periventrikuler hipotalamus akan melepaskan CRH ke hypothalamo-pituitary portal circulation yang akan memicu dikeluarkannya ACTH ke sirkulasi. ACTH akan menstimulasi keluarnya kortisol dari kelenjar adrenal. Kortisol akan menimbulkan banyak efek seperti inhibisi sistem imun, mempengaruhi metabolisme karbohidrat, lemak, protein, sistem kardiovaskuler dan lain sebagainya. Kortisol yang bersifat lipofilik ini dapat melewati sawar darah otak. Di otak hormon ini akan berikatan dengan reseptor yang mengirimkan sinyal ke hipotalamus untuk menghentikan pelepasan CRH sehingga kadar kortisol dalam darah tidak terus meningkat. (red/estiasari)

Sumber : http://catatankuliah-heri.blogspot.com/2011/03/master-of-glands.html

Pituitary gland

In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g (0.02 oz.) in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity (sella turcica) covered by a dural fold (diaphragma sellae). The pituitary is functionally connected to the hypothalamus by the median eminence via a small tube called the infundibular stem (Pituitary stalk). The pituitary fossa, in which the pituitary gland sits, is situated in the sphenoid bone in the middle cranial fossa at the base of the brain. The pituitary gland secretes nine hormones that regulate homeostasis.

Sections

The pituitary gland consists of two components: the anterior pituitary (or adenohypophysis) and the posterior pituitary (or neurohypophysis), and is functionally linked to the hypothalamus by the pituitary stalk (also named the "infundibular stem", or simply the "infundibulum"). It is from the hypothalamus that hypothalamic tropic factors are released to descend down the pituitary stalk to the pituitary gland where they stimulate the release of pituitary hormones. While the pituitary gland is known as the 'master' endocrine gland, both of the lobes are under the control of the hypothalamus; the anterior pituitary receives its signals from the parvocellular neurons and the posterior pituitary receives its signals from magnocellular neurons.[2]

Anterior pituitary (Adenohypophysis)


The anterior pituitary synthesizes and secretes the following important endocrine hormones:
Somatotropins:
  • Growth hormone (also referred to as 'Human Growth Hormone', 'HGH' or 'GH' or somatotropin), released under influence of hypothalamic Growth Hormone-Releasing Hormone (GHRH); inhibited by hypothalamic Somatostatin
Thyrotropins:
Corticotropins:
Lactotropins:
  • Prolactin (PRL), also known as 'Luteotropic' hormone (LTH), whose release is inconsistently stimulated by hypothalamic TRH, oxytocin, vasopressin, vasoactive intestinal peptide, angiotensin II, neuroprptide Y, galanin, substance P, bombesin-like peptides (gastrin-releasing peptide, neuromedin B and C), and neurotensin, and inhibited by hypothalamic dopamine.[4]
Gonadotropins:
Melanotrophins
  • Melanocyte–stimulating hormones (MSHs) or "intermedins," as these are released by the pars intermedia, which is "the middle part"; adjacent to the posterior pituitary lobe, pars intermedia is a specific part developed from the anterior pituitary lobe.

These hormones are released from the anterior pituitary under the influence of the hypothalamus. Hypothalamic hormones are secreted to the anterior lobe by way of a special capillary system, called the hypothalamic-hypophysial portal system.
The anterior pituitary is divided into anatomical regions known as the pars tuberalis, pars intermedia, and pars distalis. It develops from a depression in the dorsal wall of the pharynx (stomodial part) known as Rathke's pouch.

Posterior pituitary (Neurohypophysis)

The posterior pituitary stores and secretes the following important endocrine hormones:
Magnocellular Neurons:
Oxytocin is one of the few hormones to create a positive feedback loop. For example, uterine contractions stimulate the release of oxytocin from the posterior pituitary, which, in turn, increases uterine contractions. This positive feedback loop continues throughout labor.

Intermediate lobe

Although rudimentary in humans (and often considered part of the anterior pituitary), the intermediate lobe located between the anterior and posterior pituitary is important to many animals. For instance, in fish, it is believed to control physiological color change. In adult humans, it is just a thin layer of cells between the anterior and posterior pituitary. The intermediate lobe produces melanocyte-stimulating hormone (MSH), although this function is often (imprecisely) attributed to the anterior pituitary.

Variations among vertebrates

The pituitary gland is found in all vertebrates, but its structure varies between different groups.
The division of the pituitary described above is typical of mammals, and is also true, to varying degrees, of all tetrapods. However, only in mammals does the posterior pituitary have a compact shape. In lungfishes, it is a relatively flat sheet of tissue lying above the anterior pituitary, and, in amphibians, reptiles, and birds, it becomes increasingly well developed. The intermediate lobe is, in general, not well developed in tetrapods, and is entirely absent in birds.[5]
Apart from lungfishes, the structure of the pituitary in fish is generally different from that in tetrapods. In general, the intermediate lobe tends to be well developed, and may equal the remainder of the anterior pituitary in size. The posterior lobe typically forms a sheet of tissue at the base of the pituitary stalk, and in most cases sends irregular finger-like projection into the tissue of the anterior pituitary, which lies directly beneath it. The anterior pituitary is typically divided into two regions, a more anterior rostral portion and a posterior proximal portion, but the boundary between the two is often not clearly marked. In elasmobranchs there is an additional, ventral lobe beneath the anterior pituitary proper.[5]
The arrangement in lampreys, which are among the most primitive of all fish, may indicate how the pituitary originally evolved in ancestral vertebrates. Here, the posterior pituitary is a simple flat sheet of tissue at the base of the brain, and there is no pituitary stalk. Rathke's pouch remains open to the outside, close to the nasal openings. Closely associated with the pouch are three distinct clusters of glandular tissue, corresponding to the intermediate lobe, and the rostral and proximal portions of the anterior pituitary. These various parts are separated by meningial membranes, suggesting that the pituitary of other vertebrates may have formed from the fusion of a number of separate, but closely associated, glands.[5]
Most fish also possess a urophysis, a neural secretory gland very similar in form to the posterior pituitary, but located in the tail and associated with the spinal cord. This may have a function in osmoregulation.[5]
There is an analogous structure in the octopus brain.[6]

Functions

Hormones secreted from the pituitary gland help control the following body processes:
Pituitary gland also makes endorphin to relieve pain and alter mood.

Sumber : http://en.wikipedia.org/wiki/Pituitary_gland

Brain Parts and Function


Brain Function, It's a Team Sport


The brain is the most complex organ in the body. It is the organ that allows us to think, have emotions, move, and even dream. Given this complexity, it should not be surprising that there are many ways to separate brain parts. Brain parts can be separated on the basis of what they look like to the naked eye, under a microscope, or by what certain brain parts do. The brain and spinal cord make up the central nervous system and all of the nerves found in our body make up the peripheral nervous system. When you see a picture of the brain you probably think of a wrinkled gray blob. Well, the wrinkles are called cortex and it is where the majority of brain cells or neurons reside. The cortex can be divided into four main lobes. The frontal lobe, where you do your heavy thinking, pondering and planning your actions; temporal cortex, where you process sounds and form memories; occipital cortex, where you process all the things that you see; and parietal cortex, where you integrate or makes sense of all of the different bits of information that are bombarding your brain.

The Hindbrain

Having evolved hundreds of millions of years ago, the Hindbrain or the Reptillian Brain is the oldest part of the human brain. As you might guess from it's name, it's a piece of brain anatomy that we share with reptiles and is the most primitive. Likewise it's in charge of our primal instincts and most basic functions. Things like the instincts of survival, dominance, mating and the basic functions of respiration, heartbeat all come from this area of the brain. Located in the Hindbrain are:
  • The Spinal Cord

  • This is the infomation superhighway of the body. It carries information up to the brain and instructions back down.
  • The Medulla Oblongata

  • Helps control the body's autonomic functions (things you don't need to think about to perform) like respiration, digestion and heart rate. Also acts as a relay station for nerve signals going to/from the brain
  • The Pons

  • Has roles in your level of arousal or conciousness and sleep. Relays sensory information to/from the brain. Also involved in controlling autonomic body functions.
  • The Cerebellum

  • Mostly deals with movement. It regulates and coordinates movement, posture and balance. Also involved in learning movement.

The Limbic System

The Limbic System sometimes called the "emotional brain" or "Old Mammalian Brain" is the next brain to have evolved in the more primitive mammals about 150 million years ago. This is where our emotions reside, where memory begins and where these two functions combine together to mark behaviours with positive or negative feelings. It's where mostly unconcious value judgements are made. Information going through the Limbic System are filed under "agreeable or disagreeable". It also plays a role in salience (what grabs your attention), spontaneity and creativity. Located in the Limbic System are:
  • The Amygdala

  • It's name is latin for almond which relates to its shape. It helps in storing and classifying emotionally charged memories. It plays a large role in producing our emotions, especially fear. It's been found to trigger responses to strong emotion such as sweaty palms, freezing, increased heart-beat/respiration and stress hormone release.
  • The Hippocampus

  • This guy is all about memory and a little about learning. It's primary role is in memory formation, classifying information, long-term memory. Like the RAM in your computer it processes and stores new and temporary memory for long term storage. It's also involved in interpreting incoming nerve signals and spatial relationships.
  • The Hypothalamus

  • It should be called the Hyperthalamus because it does so much. It's linked closely with the pituitary gland to control many of the body's functions. It monitors and controls your circadian rhythms (your daily sleep/wake cycle), homeostasis (making sure your body is running smoothly), apetite, thirst, other bodily urges and also plays a role in emotions, autonomic functions and motor functions.
  • The Thalamus

  • The Thalamus is THE relay station in the brain. Most of the sensory signals, auditory (sound), Visual, Somatosensory (from your skin and internal organs), go through this organ on their way to other parts of the brain for processing. It also plays a function in motor control.

The Neocortex

The last and most advanced brain to evolve to date is called the Neocortex, neomammalian or rational brain. We share this part of our brain with other higher level mammals like the primates and dolphins, although in humans the neocortex is the largest. It takes up 2/3's of the human brain. This is where we find the brain power to develop language, abstract thought, conciousness and imagination. Let there be no doubt, this is what grants us our status on the food chain and allows us to be human.
The Neocortex is divided into two hemispheres, right and left. The right side of the brain controls the left side of the body and vice versa. Also the hemispheres are divided in terms of what kind of thought they process or produce. The right being more concerned with the artistic, spatial and musical. While the left is more concerned with the colder, linear, rational and verbal aspects. Located in the Neocortex are:
  • The Frontal Lobe

  • This is the most recent evolutionary addition to the brain. If the brain had a White House it would be here. It is the true center for command and control in your body. The Frontal lobe is responsible for functions such as reasoning, problem solving, judgement, impulse control. This coupled with the fact that it's the last to develop when we are young adults, probably answers a lot of questions for many parents out there. It also manages our higher emotions such as empathy and altruism. This lobe is also involved in motor control and memory.
  • The Parietal Lobe

  • The Parietal Lobe is involved in processing pain and touch sensation. It's where the Somatosensory (from your skin and internal organs) Cortex resides. It's also associated with cognition (including calculating location and speed of objects), movement, orientation, recognition and speech.
  • The Temporal Lobe

  • The Temporal Lobe is involved in auditory (sound) sensation and is where the Primary Auditory Cortex and on the left hemisphere, Wernicke's Area (language recognition) are located. This lobe is also involved in emotion, memory and speech.
  • The Occipital Lobe

  • The Occipital Lobe controls visual sensation and processing. The Visual Cortex is resides here.
  • Broca's Area

  • This part of the cortex controls speech, language recognition and facial nerves.
  • The Corpus Callosum

  • This is the neural bridge that connects the two hemispheres to each other, located centrally in brain.

Sumber : http://www.brainhealthandpuzzles.com/brain_parts_function.html

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