Identify an antagonistic pair of hormones and describe their action.
Why do you think the pituitary has two lobes?
What is the purpose of hormone replacement therapy?
Why might a problem with the pituitary gland affect many different parts of the body?
Your friend says that he’s pretty sure that the adrenal medulla is controlled by hormones from the pituitary. Do you agree? Explain your answer.
Outline the feedback mechanism involved in glucose metabolism. Is this feedback mechanism positive or negative?
Positive feedback mechanisms are harmful to the body. Do you agree with this statement? Explain your answer.
Goiter is a swelling of the thyroid gland, which is commonly caused by a lack of iodine in the diet. Why do you think a lack of iodine causes the thyroid to swell?
Use the image of the feedback mechanisms to answer the two questions that follow.
Figure 20.58
Identify three endocrine glands are involved in the feedback mechanisms shown in the figure.
Identify four hormones involved in these feedback mechanisms.
Further Reading / Supplemental Links
Anatomy and Physiology © 2002. Published by Benjamin Cummings, a part of Pearson Education Inc. Elaine N. Marieb.
Human Anatomy ©2003 by Fredric H. Martini, Inc. and Michael J.Timmons. Published by Pearson Education, Inc.
Biology © 2002 6th Edn. Authors: Campbell and Reese. Published by Benjamin Cummings.
Adapted from abstract: Anabolic Androgenic Steroids: A Survey of 500 Users Andrew B. Parkinson; Nick A. Evans (Medicine and Science in Sports and Exercise) at
http://www.medscape.com/viewarticle/533461
Adapted from:
http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=pubmed&dopt=AbstractPlus&list_uids=11927236
http://www.lcsc.edu/healthocc/enable03/glands/03072_3.htm
http://web.indstate.edu/thcme/mwking/peptide-hormones.html#receptors
http://web.indstate.edu/thcme/mwking/steroid-hormones.html
http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=pubmed&dopt=AbstractPlus&list_uids=15589268
http://www.nlm.nih.gov/medlineplus/ency/article/000844.htm#Definition
http://www.hormone.org/
http://www.hormone.org/
http://www.nlm.nih.gov/medlineplus/endocrinesystem
http://health.nih.gov/search.asp/24
http://www.askabiologist.org.uk/
http://en.wikipedia.org
Vocabulary
amino acid-based hormones
Hormones made of amino acids; not fat-soluble and therefore cannot diffuse through the plasma membrane of their target cell; usually bind to receptors that are found on the cell membrane.
antagonistic
Hormones that have opposite actions on the body, such as insulin and glucagons.
cholesterol-based hormones
Hormones made of lipids such as phospholipids and cholesterol; also called steroid hormones; are fat soluble and are able to diffuse through the plasma membrane; bind to receptors that are found within the cell cytosol and nucleus.
circadian rhythm
A roughly-24-hour cycle in the biological processes carried out within organisms, including plants, animals, fungi and certain bacteria.
cortisol
A steroid hormone produced by the adrenal glands; often called the "stress hormone" as it is involved in the body’s response to stress; increases blood pressure, blood sugar levels and has an immunosuppressive action.
direct gene activation
A system in which a fat-soluble hormone diffuses across the membrane and binds to the receptor within the cytosol or nucleus. The hormone-receptor complex then acts as a transcription factor that affects gene expression.
endocrine glands
Ductless organs that make and secrete hormones directly into the blood or the fluid surrounding a cell rather than through a duct.
endocrine system
A system of organs that releases chemical message molecules, called hormones, into the blood.
exocrine glands
Organs that secrete their products into ducts (they are duct glands); do not secrete hormones; secrete products such as water, mucus, enzymes, and other proteins through ducts to specific locations inside and outside the body.
feedback control mechanism
A signaling system in which a product or effect of the system controls an earlier part of the system, either by shutting the process down or speeding it up; also known as a feedback loop.
glucagon
An important hormone involved in carbohydrate metabolism; released when the glucose level in the blood is low which causes the liver to change stored glycogen into glucose and release it into the bloodstream.
gonads
The gamete producing organs; the ovaries of females and the testes of males.
hormone-like substances
Refers to a group of signaling molecules that are derived from certain types of fatty acids and proteins.
hormones
Chemical messenger molecules that are made by cells in one part of the body and cause changes in cells in another part of the body.
hypersecretion
The production of too much of a hormone.
hyposecretion
The production of no hormone or too little of a hormone.
hypothalamus
Area of the brain that coordinates many seasonal and circadian rhythms, complex homeostatic mechanisms, and the autonomic nervous system (ANS).
islets of Langerhans
Areas of the pancreas with groupings of endocrine cells; produce the amino acid-based hormones insulin, glucagon, and somatostatin.
negative feedback
A reaction in which the system responds in such a way as to reverse the direction of change.
neuropeptides
Hormone-like substance; signaling peptides found in nervous tissue.
positive feedback
A reaction in which the system responds in such a way as to speed up the direction of change.
prostaglandins
Hormone-like substance made from essential fatty acids; produced by most cells in the body; have many different effects such as causing constriction or dilation of blood vessels but they are all are localized within the target cells and tissues.
puberty
The process of physical changes during which the sex organs mature and a person become capable of reproducing.
second messenger system
A system in which a water-soluble hormone molecule does not enter the cell, instead it binds to the membrane-bound receptor molecule, which triggers changes within the cell. These changes are activated by second messenger molecules.
sex hormones
Hormones that are responsible for the secondary sex characteristics that develop at puberty.
signal transduction pathway
Process initiated by the binding of a hormone to its receptor; a process of molecular changes that turns the hormone’s extracellular signal into an intracellular response.
target cell
The cell on which a hormone has an effect; has receptor proteins that are specific to the hormone.
Points to Consider
Think about some of the problems people may have to their muscular systems if their nervous system is not functioning correctly.
Propose what would happen if the hypothalamus did not produce ADH.
Why are negative feedback loops more common than positive feedback loops?
Chapter 21: Skeletal, Muscular, and Integumentary Systems
Lesson 21.1: Skeletal System
Lesson Objectives
Identify the functions and structure of bones.
Differentiate between the axial skeleton and appendicular skeleton.
Distinguish between spongy bone and compact bone.
Outline t
he process of osteogenesis (bone formation), and how bones grow.
Classify bones based on their shape.
Identify three types of joints that are in the body, and give an example of each.
Identify three disorders that result from homeostatic imbalances of bones or the skeleton.
Introduction
How important is your skeleton? Can you imagine what you would look like without it?
You would be a wobbly pile of muscle and internal organs, maybe a little similar to the slug in Figure below. Not that you would really be able to see yourself anyway, due to the folds of skin that would droop over your eyes because of your lack of skull bones. You could push the skin out of the way, if you could only move your arms!
Figure 21.1
Banana slugs ( spp.), unlike you, can live just fine without a bony skeleton. They can do so because they are relatively small and their food source (vegetation) is plentiful and tends not to run away from them. Slugs move by causing a wave-like motion in their foot, (the ventral (bottom) area of the slug that is in contact with the ground). Slugs and other gastropods also live in environments very different to humans environments. Just think of how a bony skeleton would be of limited use to a slug whose lifetime is spent under a log munching on rotting leaf litter.
The Skeleton
Humans are vertebrates, which are animals that have a vertebral column, or backbone. Invertebrates, like the banana slug in Figure above, do not have a vertebral column, and use a different mechanism than vertebrates to move about. The sturdy internal framework of bones and cartilage that is found inside vertebrates, including humans, is called an endoskeleton. The adult human skeleton consists of approximately 206 bones, some of which are named in Figure below. Cartilage, another component of the skeleton can also be seen in Figure below. Cartilage is a type of dense connective tissue that is made of tough protein fibers. The function of cartilage in the adult skeleton is to provide smooth surfaces for the movement of bones at a joint. A ligament is a band of tough, fibrous tissue that connects bones together. Ligaments are not very elastic and some even prevent the movement of certain bones.
The skeletons of babies and children have many more bones and more cartilage than adults have. As a child grows, these “extra” bones, such as the bones of the skull (cranium), and the sacrum (tailbone) fuse together, and cartilage gradually hardens to become bone tissue.
Figure 21.2
The skeleton is the bone and cartilage scaffolding that supports the body, and allows it to move. Bones act as attachment points for the muscles and tendons that move the body. Bones are also important for protection. For example, your skull bones (cranium) protect your brain, and your ribcage protects your heart and lungs. Cartilage is the light-gray material that is found between some of the bones and also between the ribcage and sternum.
The bones of the skeleton can be grouped in two divisions: the axial skeleton and appendicular skeleton. The axial skeleton includes the bones of the head, vertebral column, ribs and sternum, in the left portion of Figure below. There are 80 bones in the axial skeleton. The appendicular skeleton includes the bones of the limbs (arms and legs) along with the scapula and the pelvis, and is shown at right in Figure below. There are approximately 126 bones in the appendicular skeleton. Limbs are connected to the rest of the skeleton by collections of bones called girdles. The pectoral girdle consists of the clavicle (collar bone) and scapula (shoulder blade). The pelvic girdle consists of two pelvic bones (hipbones) that form the pelvic girdle. The vertebral column attaches to the top of the pelvis; the femur of each leg attaches to the bottom. The humerus is joined to the pectoral girdle at a joint and is held in place by muscles and ligaments.
Figure 21.3
The two divisions of the human skeleton. The bones of the axial skeleton are blue, and the bones of the appendicular skeleton are pink.
Function and Structure of Bones
Many people think of bones as dry, dead, and brittle, which is what you might think if you saw a preserved skeleton in a museum. The association of bones with death is illustrated by the sweets shown in Figure below. This is a common association because the calcium-rich bone tissue of a vertebrate is the last to decompose after the organism dies. However, the bones in your body are very much alive. They contain many tough protein fibers, are crisscrossed by blood vessels, and certain parts of your bones are metabolically active. Preserved laboratory skeletons are cleaned with chemicals that remove all organic matter from the bones, which leaves only the calcium-rich mineralized (hardened) bone tissue behind.
Figure 21.4
Sugar skulls made to celebrate Dia de Los Muertos (Day of the Dead), a time (the 1 and 2 of November) during which the people of Mexico and some Latin American countries celebrate and honor the lives of the deceased, and celebrate the continuation of life.
Functions of Bones
As you read earlier in this lesson, your skeletal system is important for the proper functioning of your body. In addition to giving shape and form to the body, bones have many important functions.
The main functions of bones are:
Structural Support of the Body: The skeleton supports the body against the pull of gravity. The large bones of the lower limbs support the trunk when standing.
Protection of Internal Organs: The skeleton provides a rigid frame work that supports and protects the soft organs of the body. The fused bones of the cranium surround the brain to make it less vulnerable to injury. Vertebrae surround and protect the spinal cord and bones of the rib cage help protect the heart and lungs.
Attachment of the Muscles: The skeleton provides attachment surfaces for muscles and tendons which together enable movement of the body.
Movement of the Body: Bones work together with muscles as simple mechanical lever systems to produce body movement.
Production of Blood Cells: The formation of blood cells takes place mostly in the interior (marrow) of certain types of bones.
Storage of Minerals: Bones contain more calcium than any other organ in the form of calcium salts such as calcium phosphate. Calcium is released by the bones when blood levels of calcium drop too low. Phosphorus is also stored in bones.
Structure of Bones
Although bones vary greatly in size and shape, they all have certain structural similarities. Bones are organs.Recall that organs are made up of two or more types of tissues. The two main types of bone tissue are compact bone and spongy bone. Compact bone makes up the dense outer layer of bones. Spongy bone is lighter and less dense than compact bone, and is found toward the center of the bone. Periosteum (from peri = around, osteo = bone),is the tough, shiny, white membrane that covers all surfaces of bones except at the joint surfaces. Periosteum is composed of a layer of fibrous connective tissue and a layer of bone forming cells. These structures can be seen in Figure below.
Figure 21.5
Structure of a typical bone. The components that make up bones can be seen here. Compact bone is the dense material that makes up the outer ring of the bone. Most bones of the limbs are long bones, including the bones of the fingers. The classification of long bone refers to the shape of the bone rather than to the size.
Figure 21.6
The internal structure of a bone. Both compact and spongy bone can be seen.
Compact Bone
Just below the periosteum is the hard layer of compact bone tissue. It is so called due to its high density, and it accounts for about 80% of the total bone mass of an adult skeleton. Compact bone is extremely hard, and is made up of many cylinder-shaped units called osteons, or Haversian systems. Osteons act like strong pillars within the bone to give the bone strength and allow it to bear the weight of the attached muscles and withstand the stresses of movement. As you can see in Figure above, osteons are made up of rings of calcium salts and collagen fibers, called bone matrix. Bone matrix is a mixture of calcium salts, such as calcium phosphate and calcium hydroxide, and collagen fibers (a type of protein) which form hol
low tubes that look similar to the rings on a tree. Each of these matrix tubes is a lamella, which means “thin plate” (plural: lamellae). The calcium salts form crystals that give bones great strength, but the crystals do not bend easily, and tend to shatter if stressed. Collagen fibers are tough and flexible. All collagen fibers within a single lamella are lined up in the same direction, which gives each lamella great strength. Overall, the protein-calcium crystal combination in the matrix allows bones to bend and twist without breaking easily. The collagen fibers also act as a scaffold for the laying down of new calcium salts.
In the center of each osteon is a Haversian canal. The canal serves as a passageway for blood vessels and nerves. Within each osteon, many bone cells called osteocytes are located. Osteocytes are found in little pockets called lacunae that are sandwiched between layers of bone matrix. You can see lamellae and osteocytes in their lacunae in Figure 7b. Osteocytes are responsible for monitoring the protein and mineral content of the bone and they direct the release of calcium into the blood and the uptake up of calcium salts into the bone. Other bone cells, called osteoblasts secrete the organic content of matrix, and are responsible for the growth of new bone. Osteoblasts are found near the surface of bones. Osteoclasts are bone cells that remove calcium salts from bone matrix. These bone cells will be discussed in further detail later in this lesson. In the meantime, Table below describes some of the different structures and functions of bones.
CK-12 Biology I - Honors Page 100