CoverModule 1.0. Homeostasis, Membranes, Electrophysiology and ANS1.1. Homeostasis1.1.1. Homeostasis Defined1.1.2. Homeostatic Control Systems1.1.3. Feedback Response Loop1.2. Cell Transport; Water & Solutes1.2.1. Fluid Compartments1.2.2. Osmosis1.2.3. Diffusion of Solutes1.2.4. Active Transport1.2.5. Bulk Transport1.3. Electrophysiology1.3.1. Ions and Cell Membranes1.3.2. Membrane Potentials1.3.3. Graded Potential1.3.4. Action Potentials1.3.5. Refractory Periods1.3.6. Propagation of an Action Potential1.4. The Synapse1.5. The Autonomic Nervous System1.5.1. Organization of the Nervous System1.5.2. Structural Organization of the ANS1.5.3. The SNS and the PNS1.5.4. The Enteric Nervous System1.5.5. Physiology of the ANS1.5.6. Neurotransmitters of the ANS1.5.7. Receptors of the ANS1.5.8. Actions of the Autonomic Nervous System1.5.9. Table of Actions for the SNS and PNS and Some Common DrugsModule 2.0. Skeletal Muscle and Special Senses2.1. Structural Organization of Skeletal Muscle2.2.1. Neuromuscular Junction, Excitation-Contraction Coupling2.2.2. Muscle Contractures and Cramps2.3. Whole Muscle Contraction, Fiber Type, Fatigue and Muscle Pharmacology2.3.1. Motor Units2.3.2. Factors that Influence the Force of Contraction2.3.2. Factors that Influence the Force of Muscle Contraction2.3.3. Energy Source for Muscle Contraction2.3.4. Skeletal Muscle Fiber Types2.3.5. Fatigue2.3.6. Muscle Pharmacology2.4. Smooth Muscle2.4.1. Smooth Muscle Contraction2.5. Control of Body Movement2.5.1. Voluntary Control of Muscle2.5.2. Reflexes2.6. Taste and Smell2.6.1. Taste2.6.2. The Sense of Smell2.7. Vision2.7.1. Structure of the Eye2.7.2. Focusing Light on the Retina2.7.3. Converting Light to Action Potentials2.7.4. The Retina2.7.5. Phototransduction2.7.6. Receptive Fields2.8. Hearing and Equilibrium2.8.1. The Nature of Sound2.8.2. The Hearing Apparatus2.8.3. Sound Vibrations to Action Potentials2.8.4. The Sense of Balance and EquilibriumModule 3.0. Cardiovascular System3.1. Structure of the Heart3.1.1. Chambers and Circulation3.2. Cardiac Cell Action Potentials3.2.1. Action Potentials in Cardiac Muscle Cells3.2.2. Action Potentials in Cardiac Autorhythmic cells3.2.3. Cellular Mechanisms of Inotropy and Chronotropy3.3. Electrophysiology of Heart Muscle3.3.1. Heart Conduction System3.3.2. Electrocardiogram (ECG)3.3.3. Abnormal ECG - Current of Injury3.4. The Cardiac Cycle3.4.1. Cardiac cycle3.4.2. Cardiac Measurements and Pressure Volume Loops3.5. Blood vessels and Blood Pressure3.5.1. Arteries and Veins3.5.2. Capillaries3.5.3. Blood Pressure Regulation and Shock3.5.4. Capillary Exchange3.5.5. Myogenic and Paracrine Regulation of Vasoconstriction and Vasodilation3.6. Blood3.6.1. Composition of Blood3.6.2. Hematopoeisis3.6.3. Breaking Down Red Blood Cells3.6.4. HemostasisModule 4.0. Urinary and Respiratory Systems4.1. Function and Structure of the Kidney4.1.1. Urinary System Function4.1.2. Functional Anatomy of the Urinary System4.1.3. The Nephron: Functional Unit of the Kidney4.1.4. The Renal Corpuscle: Bowman's Capsule4.2. Physiology of Urine Production4.2.1. Filtration4.2.2. Renal Clearance4.2.3. Tubular Reabsorption4.2.4. Urine Concentration and Dilution4.2.5. Hormonal Regulation of Urine Production4.3. Acid/Base Balance4.3.1. Buffers4.3.2. Acid/Base Disturbances4.4. The Respiratory System4.4.1. Respiratory System Structure and Function4.4.2. Respiratory Membrane4.4.3. Respiratory pressures and Inspriation/Expiration4.4.4. Alveoli and Surfactant4.4.5. Pneumothorax4.4.6. Pressure-Volume Loops and the Work of Breathing4.5. Gas Exchange and Transport4.5.1. Gas Laws4.5.2. Partial Pressure Gradients in the Lung4.5.3. Alveolar Gas Equation4.5.4. Oxygen and Carbon Dioxide Transport in the Blood4.5.5. Alveolar Ventilation4.5.6. Ventilation/Perfusion Ratio4.6. Chronic Bronchitis and Emphysema4.6.1. Respiratory Control by the Medulla Oblongata4.6.2. Chemicals that Regulate VentilationModule 5.0. Digestive, Endocrine and Reproductive Systems5.1. Functional Anatomy of the Digestive System5.1.1. Layers of the Digestive Tract5.1.2. Enteric Nervous System5.1.3. Organs of the Digestive System5.2. Digestion5.2.1. Carbohydrates5.2.2. Proteins5.2.3. Lipids5.2.4. Lipoproteins5.3. Regulation of Digestive Secretions5.4. Endocrine System5.4.1. Overview of the Endocrine System5.4.2. Hormone Receptors5.4.3. Hormones of the Body5.4.4. Other Hormones: Melatonin and Pheromones5.5. The Hypothalamus and Pituitary Gland5.5.1. Structure and Function of the Hypothalamus and Pituitary Gland5.5.2. The Posterior Pituitary5.5.3. The Anterior Pituitary5.5.4. Growth Hormone5.5.5. Prolactin5.5.6. Thyroid Hormones5.5.7. Adrenal Hormones5.6. Pancreas5.6.1. Insulin and Glucagon5.6.2. Diabetes Mellitus5.7. Reproductive System Anatomy5.7.1. Female Reproductive Anatomy5.7.2. Male Reproductive Anatomy5.7.3. Sexual Development at Puberty5.7.4. Male Reproductive Endocrine Axis5.7.5. Spermatogenesis5.7.6. Female Reproductive System: Oogenesis5.7.7. Ovulation and Fertilization5.7.8. The Ovarian Cycle5.7.9. The Uterine Cycle5.7.10. PregnancyAppendix A. GenderAppendix B. The Placebo EffectB.2.1. The Placebo EffectB.2.2. Examples of the Placebo EffectB.2.3. How do Placebos Work?B.2.4. Are Placebos Ethical?B.2.5. How do we validate actual effectiveness of placebosB.2.6. Tips for evaluating scientific evidenceB.2.7. What about Faith Healingstest chapter

The Uterine Cycle

The uterus is where a fertilized egg will implant and develop. However, the uterus is receptive to implantation for only a short time each month. The uterine cycle is a series of events that occur to prepare the endometrium or inner lining of the uterus to be ready for possible implantation. The events of the uterine cycle are regulated by the estrogen and progesterone produced by the ovaries during the ovarian cycle.

The uterine cycle is divided into three phases: the menstrual phase (menses), the proliferative phase and the secretory phase.

Menses (Days 1-5)

Menstruation or menses is marked by the degeneration of the endometrium. The endometrium is a layer of cells, glands and blood vessels that is dependent on the ovarian hormones (estrogen and progesterone) to remain viable and healthy. In the absence of sufficient hormonal support, this layer of tissue dies and detaches from the deeper muscular layer of the uterus and sloughs off into the lumen of the uterus where it exits the body through the vaginal canal resulting in the blood and tissue flow associated with the menstrual period. The first day of menstrual bleeding is designated as day 1 of the menstrual cycle.

Proliferative (Pre-ovulatory) Phase

At the completion of menses, the functional layer of the endometrium has been sloughed off and must be replaced. The regeneration of the functional layer is under the control of estrogen. Recall that during the follicular phase of the ovarian cycle, estrogen levels increase. Estrogen stimulates stromal cells from the basal layer of the endometrium and epithelial cells that were not lost during menses (mainly from the lower portion of the uterus and near where the fallopian tube attach) to increase in number or proliferate. The stromal cells replace the connective tissue portion of the endometrium and the epithelial cells produce the glandular portion. As these cells increase in number the endometrium thickens from about 0.5 mm to about 5.0 mm. Additionally, spiral arteries arise to feed the new tissue and glandular structures develop. During this phase, estrogen also induces the endometrial cells to express large numbers of progesterone receptors in preparation for the events of the next phase of the cycle. This phase is completed at about the time of ovulation.

Secretory (Postovulatory) Phase

After ovulation, the luteal stage of the ovarian cycle gets underway and progesterone levels rise. The progesterone binds to the progesterone receptors in the endometrium. Under the influence of progesterone, the endometrial glands enlarge, coil, and begin to produce a glandular secretion high in nutritious organic molecules such as glycogen. Also, progesterone stimulates the rapid expansion of the spiral arteries in the endometrium. During the Secretory Phase, progesterone encourages the development of a very vascular and glandular endometrium capable of secreting fluids, nutrients and supplying blood to an implanted embryo. Progesterone also has an anti-estrogen effect and prevents further proliferation of the endometrial cells.

Recall that the corpus luteum degenerates at the end of the luteal stage of the ovarian cycle unless there is a pregnancy. With the degeneration of the corpus luteum, progesterone (and estrogen) levels decrease. Without this hormonal support, the spiral arteries spasm rhythmically, leading to constriction of the blood vessels reaching the endometrium. The spasms last longer and longer resulting in a reduction in levels of oxygen and the tissues become ischemic. This eventually leads to the death of the endometrial tissue and the shedding of the lining, starting the cycle again.

The image, shown again below, illustrates how the ovarian and uterine cycles are coordinated. It also demonstrates the time period involved in these cycles. While the cycles are shown on a 28-day time frame, in reality, there is great variability in cycle length. The follicular phase represents the cause of most of this variability with some research showing follicular phases ranging from 11 to 27 days. The luteal stage for most women is generally more consistent at about 14 days, although occasional variability of 7 to 15 days has been recorded (Fehring, 2006).

Uterine and Ovarian Cycle
 Image drawn by BYU-Idaho Spring 2015

End-of-Chapter Survey

: How would you rate the overall quality of this chapter?
  1. Very Low Quality
  2. Low Quality
  3. Moderate Quality
  4. High Quality
  5. Very High Quality
Comments will be automatically submitted when you navigate away from the page.
Like this? Endorse it!