Crash Course

Joanna Matthan

• Publisher: Ivy Press
• Year: 2019
• ISBN:
  9781782408604
• Topic: Biological Sciences
• Subtopic: Human Anatomy & Physiology
• Index: Biological Sciences

Anatomy: A Crash Course teaches you everything you need to know about your own anatomy, its body parts, systems, fantastic functionsand flaws. Part of the Crash Course series, the book is divided into four chapters, covering:

• The head and neck
• The chest
• The abdominopelvic region
• The back and limbs

Each chapter contains an overview and thirteen illustrated topics, each broken down into small, digestible chunks. 'Gross anatomy' depicts the features and function of the body part, while 'Clinical anatomy' reveals what happens when things go wrong. Finally, 'Dissection' provides theunusual and lesser-known secrets of our bodies. With an introduction to the history of anatomy, an illustrated timeline and biographies, plus feature spreads covering topics from the language of anatomy to electrochemical signalling, this is the perfect crash course for budding anatomists. If you like this, you might also be interested in Psychology: A Crash Course...

1
HEAD & NECK ANATOMY

“No knowledge can be more satisfactory to a man than that of his own frame, its parts, their functions and actions.”

THOMAS JEFFERSON LETTER TO DR THOMAS COOPER, 1814

NEUROENDOCRINE FUNCTION

Our brain regulates hormonal activity between the nervous system and the endocrine system, and our internal environment is regulated and controlled by a complex, yet intricate, interplay between nerves and hormones. While, within the nervous system, nerve impulses and neurotransmitters from the autonomic system relay information very quickly to the site from which a response is required, responses via the endocrine system are slower as they travel through the bloodstream in the form of hormones, taking longer to reach their target organ or site. Hormonal responses are generally slower and more widespread, though hormones can also have an effect very quickly, if needed. Indeed, some hormones produced by the endocrine system control our emotions (say, fear or stress) and are quickly dispatched to their end destination, either a gland or tissues. The first wave of hormones triggers receptors in the target tissue to release additional hormones. A complex cascade of chemical reactions then triggers a response from the nervous system and a mechanism for expressing the emotions. This is the normal way the endocrine system interacts with the nervous system. Hormones released by glands in the reproductive system have a direct effect on the development of the nervous system.

The autonomic nervous system (part of the central nervous system) and the endocrine system are both controlled by the brain—the hypothalamus in particular, which regulates hormones. The two systems act together to regulate physiological processes in the body via a process called neuroendocrine integration. This close link between the two systems is the mechanism by which the hypothalamus within the brain maintains a steady state in the body (homeostasis). It is also the way our reproductive and metabolic functions are regulated, how we consume food and water and use this energy, and how the correct composition of chemicals inside and outside our cells is maintained. It is also the way our blood pressure is controlled.

Hormone-producing glands around the body

The endocrine system is made up of a collection of glands scattered around the body which secrete chemical messengers (hormones) through the blood (but not always). The endocrine system controls these hormones that course through our arteries. Endocrine glands are generally made up of highly active cells surrounded by a rich blood supply and tissue that loosely supports them. The cells make and secrete the hormones. To trigger an effect from another site, one single hormone is not necessarily enough, and hormones may need to trigger other hormones in a cascading chain. The hormone that starts the cascade is known as a first-order hormone (releasing hormone); second-order hormones are those that have been stimulated as a result of a first-order hormone acting on them.

Perhaps our most important endocrine gland is the pituitary gland, a small pea-sized organ on the underside of the brain measuring only about 3/8 in. (1 cm) in diameter. It is sat within a saddle-shaped depression in the floor of the cranial cavity and covered by a membrane separating it and protecting it from the rest of the contents above. Its stalk protrudes through a small hole in the membrane and is attached to the hypothalamus; together they control our most basic needs. The hypothalamus controls the pituitary gland through feedback loops that can trigger the gland to start or stop hormone production. Pituitary hormones act on numerous other endocrine glands, such as the ovaries, the testes, the suprarenal (adrenal) glands, and the thyroid gland. Hormones secreted by the hypothalamus include growth hormones, oxytocin (the “love hormone”), and antidiuretic hormone (related to blood pressure). The pineal gland is sat deep within the brain and produces melatonin, a hormone that regulates our daily cycle (circadian cycle) based on periods of natural light and darkness.

Low down at the front of the neck, clinging to the sides of the trachea and overlying it by a connecting isthmus, is the butterfly-shaped thyroid gland. Its hormones regulate metabolism. Behind the thyroid gland, four pea-sized glands—the parathyroid glands—regulate calcium levels in our body. Within the abdomen, the adrenal (or suprarenal) glands located above the kidneys produce epinephrine (also known as adrenaline), preparing the body for action or the “fight or flight” response. In close proximity is the pancreas, which produces digestive enzymes but, importantly, produces hormones that regulate our sugar levels and glucose metabolism. These are insulin and glucagon. Within the scrotum in males are the testes, which produce sex hormones but also reproductive cells (sperm). The ovaries in females are at the back of the abdominal wall and produce sex hormones and reproductive cells (ova, eggs).

THE SKULL

GROSS ANATOMY | Mounted onto the vertebral column and upheld by the topmost vertebra (atlas), the skull protects the brain and sense organs within it and serves as an anchor for facial and masticatory muscles and ligaments. This bony skeleton of the head and face is a jigsaw puzzle of 22 individual bones (excluding six tiny ear bones), their saw-like jagged edges fusing developmentally via complex interlocking joints (sutures). The sutured bones form three small cavities (one nasal and two orbital cavities), one larger ovoid cranial cavity for the brain, and numerous smaller cavities, some of which are air-filled spaces. Only the tooth-filled lower jaw is movable; the other 21 bones are firmly knit-together. The fetal skull, though, is pliable and allows remodeling during the birthing process; incomplete bony fusion leaves soft membranous gaps that permit expansion, ensuring sufficient space for growth without damage to the rapidly growing nervous system. The skull is rarely completely symmetrical. Its sides are somewhat flattened, and its undersurface uneven and littered with numerous openings for transmitting the spinal cord, blood vessels and nerves. The smooth convex contours of the skullcap (skull vault) shielding the brain distribute any impact widely, minimizing the likelihood of fractures. The uneven facial skeleton, formed by 14 bones, exhibits wide individual variation.

Frontal View

Lateral View

Mid-sagittal view

CLINICAL ANATOMY | X-rays can often differentiate between the crooked line of a suture and the straighter line of a skull fracture. The midline (metopic) suture in the forehead normally disappears in childhood, giving the appearance of a uniform bone; if it remains, this suture may be mistaken for a fracture. The pterion is an H-shaped junction at the temples at which four bones interlock. Covered in life by thick muscle, the underlying bone is surprisingly thin and vulnerable; a blow can rupture the artery behind it and subsequent build-up of blood within the skull results in rapid death. Elastic young skulls yield more when injured, resulting in damage to the brain without necessarily fracturing bone.

DISSECTION | Skull sutures are so tightly knit together they cannot be pulled apart forcefully, even after death, without damaging the multilevel interlocking system. So, anatomists used to fill the skull with dried chickpeas through its largest opening. With the skull left to soak in water over a few days, the expanding chickpeas would gently tease apart the interlocking mechanism and the individual skull bones could be separated but remain intact for later examination.

CRANIAL CAVITY & MENINGES

GROSS ANATOMY | Two large, paired and four single bones fuse to form the cranial cavity lodging the brain. A peek into the skull reveals an uneven floor that reflects structures overlying and m...

Table of contents

• Cover
• Title Page
• Contents
• Introduction
• 1 Head & Neck Anatomy
• 2 Thoracic Anatomy
• 3 Abdominopelvic Anatomy
• 4 Back & Limb Anatomy
• Glossary
• Further Reading
• Index
• About the Author
• Acknowledgments
• Copyright